slate locust
PROXIMITY SETUP:
Any AI character could setup an invisible Proximity Point, to places, where the player was mostly seen.
After doing at least one of his casual built-in proximity, he could choose to walk towards one of his placed Proximity Points, to check/guard them for a while. (make it like the bear traps places, to make it work for the AI to place the proximity point)
BETTER HEARING:
They should hear sounds like 'Opening doors, Picking up an Item, Doing practically nearly any sound action'
But make it, so some of the sounds trigger only the 'Hearing Action' (when the enemy is stuck in the hearing animation, to hear any new sound, I hope I described it well enough ._. )
PHOTOGRAPHIC MEMORY:
They can notice opened doors, openable windows, secret paintings... ANYTHING that is 'actionable' or movable.
!!PLEASE MAKE THEM ALSO TO CHECK WARDROBES!! 
This could be too much to add, or hard, or it would make AIs too OP... I don't think it would make an AIs OP, it would make them more advanced and it would show, that this game is actually professional (I mean, it already is :3 ) and it would make AIs more of a threat, because they already get stuck during chases, or they lose you easily... so what... ._.
But I still love this game and franchise in a whole, and this is just an improvement :33
I hope that you enjoyed this bible 
tranquil venture