Chaos Inoculation Confusion? Please help.

So I just tried it and while fighting the Brambleghast (which is a chaos / phys fight) on a T5 map. I Kept getting 1 shot. On my last attempt I speced out again and with just 20 chaos res it was a breeze. Am I missing something?

Chaos Inoculation doesn't make you immune to phys. Only to chaos.

Things like poison dot, bleeding, all the purple plant mechanics, and any purple-colored spells.

Typically you wanna offset CI with something like a big energy shield or use Mind over Matter to have a big mana pool as hp