Question on enemy Breton stats

[Chicken Slayer]

I've been testing some bow designs (reloading the auto-save and playing the same dungeon over and over) and in doing so it has become clear that the brown haired Breton mages/necromancers (both male and female) react differently than the old guy/Joffrey version. I am hitting them with one second Drain Speed + weakness to poison + weakness to magic and trying to follow it with a poisoned shot from the same bow. The brown-haired versions are much more difficult to hit with the second shot due to movement before the second shot. They do not stun as well as the old guys and recover with more aggression. They see me and attack. It wasn't so bad at lower levels, but I'm really noticing it now at level 18.
I wonder if they have a higher sneak stat and/or whatever stat causes aggression.