chaos inoculation confusion?

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?

See: https://poe2db.tw/us/The_Brambleghast

That should explain it. Most of his attacks are physical, and the chaos orb is only 60% chaos conversion. It's because you don't have chaos resist in the campaign, so campaign enemies seldom deal chaos damage and even some attacks that have chaos visuals are not chaos. This is confusing when you get to maps and chaos damage becomes a significant factor.