So I got an item that gives me +390 Max HP from a Level 1 mob and I'm like 90% sure that's not supposed to happen

Yea, the items need work....lol.

Sounded like from livestream enhancement changes are coming.

I have a feeling that, for now, the enhancements table is populated by only a few fixed combinations of enhancement type and modification factor. Otherwise it would be really odd to get multiple drops that mod your regen by exactly 19.58%, or whatever.