I've been doing more random sweeps to try and diagnose this and stumbled upon this which seems to make a very large fast worm very angry. It doesn't appear to be a kill frequency but it does appear to slowly injure it. Any one have any idea what it might be?
This is the sweep I generated around it if anyone wants to test. Note though the range is much much wider than 10. It's more like 100, or 1000.
The full sweep I discovered it in is also below if you want to test.
sweep 47500.7656 67700.7656 1
Lastly, thanks to newports for the extra digits/penetration idea. Even with wide integer sweeps having non zero decimal places appears to make the hit stronger.