Is there a predictable movement pattern for deer and elk?

From my observations, startled animals will not flee you to the end of Nirn. It is safe to assume they will attempt to put a certain distance between you. On a level plane, I am willing to bet they would be fleeing directly away from you, however in the real (imaginary) world they will have to route around obstacles, otherwise the first tree directly in front of them would stop their flight. Every n milliseconds, their Ai will adjust their heading to account for your position and any obstacles. As they turn, they will decrease speed. They will also slow down and stop after they have managed to distance themselves enough from you. I very much doubt the AI actually tracks your aiming, as I haven't observed them moving any more erratically when being aimed at than necessary to run away while navigating around obstacles, not to mention that it would be unrealistic. If you cannot reliably kill them with projectile attacks, i would suggest either using AOE attacks (fireballs) or letting them run away and shooting them once they've stopped.