Ignore def doesn't stack

Isn't it 35% of the monsters def(In this case, 25)? So 35% of 25 = 8.75% defense ignored. There's a reason why people say ignoring high PDRate(50%+) bosses is more beneficial

I know that which ends up leaving the monster with 65% of their original def left, as you can see in the math I did 25*0.65 = 16.25% def leftover meaning I should have 83.75% of my range dmg, however with my range*total dmg boost*def reduction the lowest I should hit would be 38315