Ignore Def % Limit?

Someone once told me that ignore pdr does not stack. I will show you what I mean.

Let's say I am fighting PB, which has 70% PDR, right?

Well if I go and attack it since I have 112% ignore.

30% from my bow
21% nebulite
6% Ambition
30% leafre set
25% from marksmanship

Alright so out of that 30% and 30% are the highest ignores I have so what someone told me it does is this:

70%-30% = 49% - 30% =34.3 - 25% = 25.725 = 20.32275 - 6% = 19.013385%

Ignore def % is additive. If you have that much ignore, you can test it on Azwan hell mode mobs (70% pdr) to confirm that your damage isn't getting reduced. My Blaze is hitting the same on those and orange mushrooms, so it appears that it's additive for me.