diff --git a/.github/actions/test-setup/action.yml b/.github/actions/test-setup/action.yml
index 754e55d..866f3da 100644
--- a/.github/actions/test-setup/action.yml
+++ b/.github/actions/test-setup/action.yml
@@ -26,6 +26,10 @@ inputs:
     description: The branch on the site repository that mirrors the config repository.
     type: string
     required: true
+  test_site_repo_live_branch:
+    description: The name of the live branch (ie the one that's currently deployed).
+    type: string
+    required: true
   test_site_repo_pr_branch:
     description: The name of the topic branch to create on the site repository with config changes.
     type: string
@@ -61,6 +65,7 @@ runs:
         git config --global user.name 'Test User'
         git config --global user.email 'test@example.com'
 
+        # Create the main branch on the config repo with two commits.
         pushd remote
         git checkout --orphan ${{ inputs.test_config_repo_branch }}-new
         git rm -rf .
@@ -72,22 +77,30 @@ runs:
         git add c e
         git rm d
         git commit -m "Updated"
-        git push origin HEAD:${{ inputs.test_config_repo_branch }} --force
+        git push origin HEAD:${{ inputs.test_config_repo_branch }}
         git checkout ${{ inputs.test_config_repo_branch }}
         git reset --hard origin/${{ inputs.test_config_repo_branch }}
         popd
 
+        # Add the mock site with current config to staging and main.
         pushd site
         git checkout --orphan ${{ inputs.test_site_repo_pr_branch_base }}-new
         git rm -rf .
         mkdir -p a z config/sync
         cp -r ../remote/* config/sync
         touch {a,z}/.gitkeep b
-        git config user.name 'Test User'
-        git config user.email 'test@example.com'
         git add .
         git commit -m "Add mock Drupal site"
-        git push origin HEAD:${{ inputs.test_site_repo_pr_branch_base }} --force
+        
+        git branch ${{ inputs.test_site_repo_live_branch }}
+        git push origin ${{ inputs.test_site_repo_live_branch }}
+        
+        # Add an extra commit to staging only with an additional config change.
+        echo modified > config/sync/e
+        git add config/sync
+        git commit -m "Simulate updating config during development"
+        git push origin HEAD:${{ inputs.test_site_repo_pr_branch_base }}
+        
         git checkout ${{ inputs.test_site_repo_pr_branch_base }}
         git reset --hard origin/${{ inputs.test_site_repo_pr_branch_base }}
         popd
diff --git a/.github/actions/test-teardown/action.yml b/.github/actions/test-teardown/action.yml
index b56ab1a..195d832 100644
--- a/.github/actions/test-teardown/action.yml
+++ b/.github/actions/test-teardown/action.yml
@@ -12,10 +12,16 @@ runs:
   steps:
     - name: Tear down for test
       shell: bash
-      working-directory: test/site
+      working-directory: test
       run: |
-        # Tear down for test
         set -eu
-        git for-each-ref "refs/remotes/origin/${{ inputs.branch_prefix }}*" --format '%(refname:short)' | while read refname
-          do git push -d origin ${refname//'origin/'/}
+        # Tear down for test
+        for directory in remote site; do
+          pushd "$directory"
+          git for-each-ref "refs/remotes/origin/${{ inputs.branch_prefix }}*" --format '%(refname:short)' | while read refname; do
+            branch=${refname//'origin/'/}
+            git push -d origin $branch
+            echo "Deleted $directory branch '$branch'."
+          done
+          popd
         done
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 8f211a7..0065305 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -37,6 +37,7 @@ jobs:
     env:
       test_config_repo_branch: "${{ github.job }}-main"
       test_site_repo_config_branch: "${{ github.job }}-config-only"
+      test_site_repo_live_branch: "${{ github.job }}-main"
       test_site_repo_pr_branch: "${{ github.job }}-automatic-config-export"
       test_site_repo_pr_branch_base: "${{ github.job }}-staging"
     steps:
@@ -54,6 +55,7 @@ jobs:
           test_site_repo: ${{ vars.TEST_SITE_REPO }}
           test_site_repo_token: ${{ secrets.TEST_SITE_REPO_TOKEN }}
           test_site_repo_config_branch: ${{ env.test_site_repo_config_branch }}
+          test_site_repo_live_branch: ${{ env.test_site_repo_live_branch }}
           test_site_repo_pr_branch: ${{ env.test_site_repo_pr_branch }}
           test_site_repo_pr_branch_base: ${{ env.test_site_repo_pr_branch_base }}
 
@@ -65,6 +67,7 @@ jobs:
           site_repo: ${{ vars.TEST_SITE_REPO }}
           site_repo_token: ${{ secrets.TEST_SITE_REPO_TOKEN }}
           site_repo_config_branch: ${{ env.test_site_repo_config_branch }}
+          site_repo_live_branch: ${{ env.test_site_repo_live_branch }}
           site_repo_pr_branch: ${{ env.test_site_repo_pr_branch }}
           site_repo_pr_branch_base: ${{ env.test_site_repo_pr_branch_base }}
 
@@ -104,6 +107,7 @@ jobs:
       test_site_repo_config_branch: "${{ github.job }}-config-only"
       test_site_repo_pr_branch: "${{ github.job }}-automatic-config-export"
       test_site_repo_pr_branch_base: "${{ github.job }}-staging"
+      test_site_repo_live_branch: "${{ github.job }}-main"
     steps:
 
       - uses: actions/checkout@v4
@@ -119,6 +123,7 @@ jobs:
           test_site_repo: ${{ vars.TEST_SITE_REPO }}
           test_site_repo_token: ${{ secrets.TEST_SITE_REPO_TOKEN }}
           test_site_repo_config_branch: ${{ env.test_site_repo_config_branch }}
+          test_site_repo_live_branch: ${{ env.test_site_repo_live_branch }}
           test_site_repo_pr_branch: ${{ env.test_site_repo_pr_branch }}
           test_site_repo_pr_branch_base: ${{ env.test_site_repo_pr_branch_base }}
 
@@ -129,17 +134,27 @@ jobs:
           cd site
           git remote add remote-config ../remote
           git fetch remote-config
+          # Create the site repo config-only branch 1 commit behind the config repo.
           git checkout -b ${{ env.test_site_repo_config_branch }} remote-config/${{ env.test_config_repo_branch }}^
           tmp_dir=$(mktemp -d)
           cp * "$tmp_dir"
           git push origin HEAD
           
-          git checkout ${{ env.test_site_repo_pr_branch_base }}
+          # Ensure the live branch matches the new site repo config branch.
+          git checkout ${{ env.test_site_repo_live_branch }}
           rm config/sync/*
-          cp -r "$tmp_dir"/* config/sync
-          git add .
+          mv "$tmp_dir"/* config/sync
+          git add config/sync
           git commit --amend -m "Update"
-          git push origin HEAD --force
+          git push --force origin HEAD
+          
+          # Update the staging branch with a fresh config change.
+          git checkout ${{ env.test_site_repo_pr_branch_base }}
+          git reset --hard ${{ env.test_site_repo_live_branch }}
+          echo modified > config/sync/e
+          git add config/sync/e
+          git commit -m "Simulate updating config during development"
+          git push --force
 
       - uses: ./test/update-config
         with:
@@ -149,6 +164,7 @@ jobs:
           site_repo: ${{ vars.TEST_SITE_REPO }}
           site_repo_token: ${{ secrets.TEST_SITE_REPO_TOKEN }}
           site_repo_config_branch: ${{ env.test_site_repo_config_branch }}
+          site_repo_live_branch: ${{ env.test_site_repo_live_branch }}
           site_repo_pr_branch: ${{ env.test_site_repo_pr_branch }}
           site_repo_pr_branch_base: ${{ env.test_site_repo_pr_branch_base }}
 
@@ -168,24 +184,23 @@ jobs:
         run: |
           set -eu
           exit=0
-          tmp_dir=$(mktemp -d)
-          git checkout ${{ env.test_site_repo_config_branch }}
-          cp * "$tmp_dir"
           
-          git checkout ${{ env.test_site_repo_pr_branch }}
-          if [[ "$(gh pr list --json id)" == "[]" ]]; then
+          if [[ "$(gh pr list --head ${{ env.test_site_repo_pr_branch }} --json id)" == "[]" ]]; then
             echo "**TEST FAILURE:** There should be a PR created." >> "$GITHUB_STEP_SUMMARY"
             exit=1
           fi
           
-          rm config/sync/*
-          mv "$tmp_dir"/* config/sync
-          if [[ -n "$(git status --porcelain)" ]]; then
-            echo "**TEST FAILURE:** The PR branch config should match the config repo branch." >> "$GITHUB_STEP_SUMMARY"
-            exit=1          
+          git checkout ${{ env.test_site_repo_pr_branch_base }}
+          git merge origin/${{ env.test_site_repo_pr_branch }}
+          if [[ "$(cat config/sync/c)" != "modified" ]]; then
+            echo "**TEST FAILURE:** After merging the config PR the 'c' file is incorrect." >> "$GITHUB_STEP_SUMMARY"
+            exit=1
           fi
           
-          rm -rf "$tmp_dir"
+          if [[ "$(cat config/sync/e)" != "modified" ]]; then
+            echo "**TEST FAILURE:** After merging the config PR the 'e' file is incorrect." >> "$GITHUB_STEP_SUMMARY"
+            exit=1
+          fi
           
           exit $exit
 
@@ -201,6 +216,7 @@ jobs:
     env:
       test_config_repo_branch: "${{ github.job }}-main"
       test_site_repo_config_branch: "${{ github.job }}-config-only"
+      test_site_repo_live_branch: "${{ github.job }}-main"
       test_site_repo_pr_branch: "${{ github.job }}-automatic-config-export"
       test_site_repo_pr_branch_base: "${{ github.job }}-staging"
     steps:
@@ -218,6 +234,7 @@ jobs:
           test_site_repo: ${{ vars.TEST_SITE_REPO }}
           test_site_repo_token: ${{ secrets.TEST_SITE_REPO_TOKEN }}
           test_site_repo_config_branch: ${{ env.test_site_repo_config_branch }}
+          test_site_repo_live_branch: ${{ env.test_site_repo_live_branch }}
           test_site_repo_pr_branch: ${{ env.test_site_repo_pr_branch }}
           test_site_repo_pr_branch_base: ${{ env.test_site_repo_pr_branch_base }}
 
@@ -262,6 +279,7 @@ jobs:
           site_repo: ${{ vars.TEST_SITE_REPO }}
           site_repo_token: ${{ secrets.TEST_SITE_REPO_TOKEN }}
           site_repo_config_branch: ${{ env.test_site_repo_config_branch }}
+          site_repo_live_branch: ${{ env.test_site_repo_live_branch }}
           site_repo_pr_branch: ${{ env.test_site_repo_pr_branch }}
           site_repo_pr_branch_base: ${{ env.test_site_repo_pr_branch_base }}
 
@@ -300,6 +318,7 @@ jobs:
       test_site_repo_config_branch: "${{ github.job }}-config-only"
       test_site_repo_pr_branch: "${{ github.job }}-automatic-config-export"
       test_site_repo_pr_branch_base: "${{ github.job }}-staging"
+      test_site_repo_live_branch: "${{ github.job }}-main"
     steps:
 
       - uses: actions/checkout@v4
@@ -315,20 +334,20 @@ jobs:
           test_site_repo: ${{ vars.TEST_SITE_REPO }}
           test_site_repo_token: ${{ secrets.TEST_SITE_REPO_TOKEN }}
           test_site_repo_config_branch: ${{ env.test_site_repo_config_branch }}
+          test_site_repo_live_branch: "${{ github.job }}-main"
           test_site_repo_pr_branch: ${{ env.test_site_repo_pr_branch }}
           test_site_repo_pr_branch_base: ${{ env.test_site_repo_pr_branch_base }}
 
       - name: 'Test setup for testing matching config'
-        working-directory: test
+        working-directory: test/site
         run: |
           set -eu
-          cd site
           git remote add remote-config ../remote
           git fetch remote-config
           git checkout -b ${{ env.test_site_repo_config_branch }} remote-config/${{ env.test_config_repo_branch }}^
-          tmp_dir=$(mktemp -d)
-          cp * "$tmp_dir"
-          git push origin HEAD
+          #tmp_dir=$(mktemp -d)
+          #cp * "$tmp_dir"
+          #git push origin HEAD
 
       - uses: ./test/update-config
         with:
@@ -338,6 +357,7 @@ jobs:
           site_repo: ${{ vars.TEST_SITE_REPO }}
           site_repo_token: ${{ secrets.TEST_SITE_REPO_TOKEN }}
           site_repo_config_branch: ${{ env.test_site_repo_config_branch }}
+          site_repo_live_branch: ${{ env.test_site_repo_live_branch }}
           site_repo_pr_branch: ${{ env.test_site_repo_pr_branch }}
           site_repo_pr_branch_base: ${{ env.test_site_repo_pr_branch_base }}
 
@@ -357,9 +377,9 @@ jobs:
         run: |
           set -eu
           exit=0
-          tmp_dir=$(mktemp -d)
-          git checkout ${{ env.test_site_repo_config_branch }}
-          cp * "$tmp_dir"
+          #tmp_dir=$(mktemp -d)
+          #git checkout ${{ env.test_site_repo_config_branch }}
+          #cp * "$tmp_dir"
           
           if [[ "$(gh pr list --head ${{ env.test_site_repo_pr_branch }} --json id)" != "[]" ]]; then
             echo "**TEST FAILURE:** There should not be a PR created." >> "$GITHUB_STEP_SUMMARY"
@@ -367,14 +387,18 @@ jobs:
           fi
           
           git checkout ${{ env.test_site_repo_pr_branch_base }}
-          rm config/sync/*
-          mv "$tmp_dir"/* config/sync
-          if [[ -n "$(git status --porcelain)" ]]; then
-            echo "**TEST FAILURE:** The site staging branch should match the config repo branch." >> "$GITHUB_STEP_SUMMARY"
-            exit=1          
+          
+          if [[ "$(cat config/sync/c)" != "modified" ]]; then
+            echo "**TEST FAILURE:** The PR base branch doesn't contain the updated file 'c'." >> "$GITHUB_STEP_SUMMARY"
+            exit=1
           fi
           
-          rm -rf "$tmp_dir"
+          if [[ "$(cat config/sync/e)" != "modified" ]]; then
+            echo "**TEST FAILURE:** The PR base branch doesn't contain the updated file 'e'." >> "$GITHUB_STEP_SUMMARY"
+            exit=1
+          fi
+          
+          #rm -rf "$tmp_dir"
           
           exit $exit
 
diff --git a/README.md b/README.md
index e3c286d..aca52fd 100644
--- a/README.md
+++ b/README.md
@@ -89,6 +89,10 @@ with:
   # The branch on the site repository that mirrors the config repository.
   # Default: config-only
   site_repo_config_branch: ''
+
+  # The name of the live branch (ie the one that's currently deployed).
+  # Default: main
+  site_repo_live_branch: ''
   
   # The name of the topic branch to create on the site repository with config
   # changes.
diff --git a/action.yml b/action.yml
index d2631c7..5404839 100644
--- a/action.yml
+++ b/action.yml
@@ -40,6 +40,11 @@ inputs:
     type: string
     required: true
     default: config-only
+  site_repo_live_branch:
+    description: The name of the live branch (ie the one that's currently deployed).
+    type: string
+    default: main
+    required: true
   site_repo_pr_branch:
     description: The name of the topic branch to create on the site repository with config changes.
     type: string
@@ -167,7 +172,7 @@ runs:
         set -eu
         source_branch=${{ inputs.site_repo_pr_branch }}
         if ! git show-branch remotes/origin/${{ inputs.site_repo_pr_branch }} &> /dev/null; then
-          git branch ${{ inputs.site_repo_pr_branch }} origin/${{ inputs.site_repo_pr_branch_base }}
+          git branch ${{ inputs.site_repo_pr_branch }} origin/${{ inputs.site_repo_live_branch }}
           source_branch=${{ inputs.site_repo_pr_branch_base }}
         fi
         git checkout ${{ inputs.site_repo_pr_branch }}
diff --git a/workflow-templates/update-config-branch.yml b/workflow-templates/update-config-branch.yml
index 4045c6c..185004f 100644
--- a/workflow-templates/update-config-branch.yml
+++ b/workflow-templates/update-config-branch.yml
@@ -13,6 +13,8 @@ name: Check for config updates
 # - CONFIG_REPO: The GitHub config repo, eg. MyOrg/MySiteConfig.
 # - SITE_REPO_PR_BRANCH_BASE: (optional) The branch from which the config topic
 #   branch will be made for the PR; defaults to 'staging'.
+# - SITE_REPO_LIVE_BRANCH: (optional) The name of the live branch (ie the one
+#   that's currently deployed).
 # - GITHUB_NOTIFY: (optional) A space-separated list of github users including
 #   '@' to ping on a new PR, eg. '@andy @becca'.
 
@@ -38,3 +40,4 @@ jobs:
           config_repo_token: ${{ secrets.CONFIG_REPO_TOKEN }}
           github_notify: ${{ vars.GITHUB_NOTIFY }}
           site_repo_pr_branch_base: ${{ vars.SITE_REPO_PR_BRANCH_BASE || 'staging' }}
+          site_repo_live_branch: ${{ vars.SITE_REPO_LIVE_BRANCH || 'main' }}