IIRC (and I very well may not, or things may have changed), for the factors that can change throughout the game, the AI hacking response is proportional to (in rough order of magnitude of influence):
-Current hacking progress (response goes down as HaP goes up)
-Total spent hacking progress (response goes up as total spent goes up)
-How much HaP the next of the current hack type can add (response goes up as this goes up); this is tied to how many of that kind of hack you have done previously