Skiff Guard's Trust Agent ability

Skiff Guard's Trust Agent ability can stack up to 5 times. However, the description does not indicate that the +30% defense penetration and offense stacks. It seems to me that it should, otherwise there doesn't seem to be a benefit of having more than 1 stack.

I tried to do some testing but couldn't say for sure that I was seeing a dmg increase with more stacks.

Does anyone know for sure if the defense penetration and offense stacks?

Thanks!

Be Wary out there...