Hm, observation of the day: looks like some AI parts hardwired directly into difficulty level, no matter what additional options are chosen:
For example, when comparing default Hard against Core + Additional Enemies Behaviors on, it is quite noticeable that some kind of the "Smart" targeting taking the place - melees are lot less willing to continue whacking invulnerable dogs/horses/dinosaurs and move on to easier target in 1-2 rounds. And ranges often target rider instead of his mount or just have a huge hate boner for the party member with the least AC. Really, on Core, Ember was never shot at often enough to tempt me to take Pranked Beneficial Curse on her for the Mirror Image, but on Hard it is no longer the case.
And its seems that it worked similarly in Kingmaker, I just had not played on below Hard often enough to notice.