I notice the following problems:

-The further you are, the higher the chance the bullets will not get a hit detection. The problem that may be causing this is that the further you are from the target the less acurate the position of an enamy is. You often see them skip from spot to spot.

-Uncertain ground: usually if an enamy is on the slope they start clipping through the ground and than you really are playing a guessing game of where to shoot them. Usually they can not be shot unless random luck turns your way.

I can make videos if needed.