diff --git a/src/dilax/effect.py b/src/dilax/effect.py
index 2095b3a..e234199 100644
--- a/src/dilax/effect.py
+++ b/src/dilax/effect.py
@@ -95,7 +95,6 @@ def __init__(
         self.up = up  # +1 sigma
         self.down = down  # -1 sigma
 
-    @eqx.filter_jit
     def vshift(self, sf: jax.Array, sumw: jax.Array) -> jax.Array:
         factor = sf
         dx_sum = self.up + self.down - 2 * sumw
@@ -121,8 +120,10 @@ def constraint(self) -> HashablePDF:
 
     def scale_factor(self, parameter: Parameter, sumw: jax.Array) -> jax.Array:
         sf = parameter.value
-        # clip, no negative values are allowed
-        return jnp.maximum((sumw + self.vshift(sf=sf, sumw=sumw)) / sumw, 0.0)
+        shift = self.vshift(sf=sf, sumw=sumw)
+        # handle zeros, see: https://github.com/google/jax/issues/5039
+        x = jnp.where(sumw == 0.0, 1.0, sumw)
+        return jnp.where(sumw == 0.0, 1.0, (x + shift) / x)
 
 
 class lnN(Effect):
diff --git a/src/dilax/modifier.py b/src/dilax/modifier.py
index 81c2f06..c99ba4b 100644
--- a/src/dilax/modifier.py
+++ b/src/dilax/modifier.py
@@ -173,6 +173,8 @@ class staterror(ModifierBase):
     """
     Create a staterror (barlow-beeston) modifier which acts on each bin with a different _underlying_ modifier.
 
+    *Caution*: The instantiation of a `staterror` is not compatible with JAX-transformations (e.g. `jax.jit`)!
+
     Example:
 
     .. code-block:: python
@@ -188,7 +190,7 @@ class staterror(ModifierBase):
 
         # all bins with bin content below 10 (threshold) are treated as poisson, else gauss
         modify = dlx.staterror(
-            parameters=[p1, p2, p3],
+            parameters={1: p1, 2: p2, 3: p3},
             sumw=hist,
             sumw2=hist,
             threshold=10.0,
@@ -272,15 +274,7 @@ def _mod(
         _poisson_mod = partial(_mod, effect=poisson)
         _gauss_mod = partial(_mod, effect=gauss)
 
-        # if all true in mask use poisson
-        if jnp.all(self.mask):
-            return jax.vmap(_poisson_mod)(values, _widths, idxs)
-
-        # if all false in mask use gauss
-        if jnp.all(~self.mask):
-            return jax.vmap(_gauss_mod)(values, _widths, idxs)
-
-        # if mixed use jnp.where
+        # apply
         return jnp.where(
             self.mask,
             jax.vmap(_poisson_mod)(values, _widths, idxs),
@@ -290,7 +284,9 @@ def _mod(
 
 class autostaterrors(eqx.Module):
     class Mode(eqx.Enumeration):
-        poisson = "Poisson per process and bin"
+        barlow_beeston_full = (
+            "Barlow-Beeston (full) approach: Poisson per process and bin"
+        )
         poisson_gauss = "Poisson (Gauss) per process and bin if sumw < (>) threshold"
         barlow_beeston_lite = "Barlow-Beeston (lite) approach"
 
@@ -298,7 +294,7 @@ class Mode(eqx.Enumeration):
     sumw2: dict[str, jax.Array]
     masks: dict[str, jax.Array]
     threshold: float
-    mode: str = eqx.field(static=True)
+    mode: str
     key_template: str = eqx.field(static=True)
 
     def __init__(
@@ -340,7 +336,7 @@ def prepare(
         Helper to automatically create parameters used by `staterror`
         for the initialisation of a `dlx.Model`.
 
-        _Caution_: This function is not compatible with JAX-transformations (e.g. `jax.jit`)!
+        *Caution*: This function is not compatible with JAX-transformations (e.g. `jax.jit`)!
 
         Example:
 
@@ -364,7 +360,7 @@ def prepare(
                     sumw=sumw,
                     sumw2=sumw2,
                     threshold=10.0,
-                    mode=dlx.autostaterrors.Mode.poisson,
+                    mode=dlx.autostaterrors.Mode.barlow_beeston_full,
                 )
                 parameters, staterrors = auto.prepare()
 
@@ -387,6 +383,7 @@ def prepare(
 
         parameters: dict[str, dict[str, Parameter]] = {}
         staterrors: dict[str, dict[str, eqx.Partial]] = {}
+
         for process, _sumw in self.sumw.items():
             key = self.key_template.format(process=process)
             process_parameters = parameters[key] = {}
@@ -405,11 +402,13 @@ def prepare(
                 "sumw2": self.sumw2[process],
                 "threshold": self.threshold,
             }
-            if self.mode == self.Mode.poisson:
+            if self.mode == self.Mode.barlow_beeston_full:
                 kwargs["threshold"] = jnp.inf  # inf -> always poisson
             elif self.mode == self.Mode.barlow_beeston_lite:
                 kwargs["sumw"] = jnp.where(
-                    mask, _sumw, sum(jax.tree_util.tree_leaves(self.sumw))
+                    mask,
+                    _sumw,
+                    sum(jax.tree_util.tree_leaves(self.sumw)),
                 )
                 kwargs["sumw2"] = jnp.where(
                     mask,