Speed drops during aggregation, low throughput

[SriramScorp]

Am running glorytun UDP version 0.3.4 and trying to aggregate two WANs—one wireline broadband giving 60-70Mbps and a USB modem giving 10-15Mbps. When path is created with either of the WANs, I get speeds of 40-50Mbps and 8-10Mbps respectively. But, when path is created for both WANs simultaneously, transfer rate on wireline broadband drops to match USB speeds, and can only achieve a throughput of 13-18Mbps. Most times, download speeds are much lower at 5-8Mbps while upload speeds are comparatively better at 16-20Mbps. How to increase speeds such that throughput is the combined speeds of both WANs?

[TalalMash]

Experiment with weight per link, make sure to set them instead of auto.
When doing speed tests, try parallel/multiple streams first.