%boss dmg not working?

With the final Demon Lash upgrade, the first attack should do 380% right? (100 + 280)

Assuming that's right, I hit below my minimum range, even with 10% defense accounted in, with 0% pdr.

Edit:
Tested Demon Lash and Demon Impact on normal and dojo bosses, and accounting for pdr I found:

with Demon Lash, Almost no increase, ~10%
with DemonImpact(lvl 1, 1%boss), ~50% increase.

I have 50% boss atm, 10% from skill, and a weapon with 20 and 20. Which all stacks at least with Demon Impact.