AC and damage reduction (in General)

I've tried looking this up in wiki but still can't figure out why there is such a huge difference in reduction or what seems like no reduction.

Slayer's minion commander has 460 ac. Steel skin is not a factor as it fizzles. My Hal hits him for about as much as he would against 0 ac about 1.2m average.

Nems minion tesla coil has 302 ac. Again steel skin fizzles. Hal hits for around 600k and that looks right around 50% reduction.

What have I missed?

He is over the minions enc.

Your DM leaves me at 76AC after encumbrance.

That was to easy. Thanks for clearing that up.

Wait until we test it on my char...