I suggest trying out the "Auto" positioning as well if you haven't yet. It will automatically target feet with rockets & pipes, so the target is more likely to become airborne from the blast, and when the target is not on ground it will aim at the center of the body. Arrows under "Auto" will always prefer head, and stickies are also attempted to be shot directly to the ground next to them. (the target position for pipes and rockets is also accounted during running the simulation, if the target is simulated to be airborne during impact, center body will be the target, if not then again, feet are the priority target). The reason for preferring feet on ground is as I said, to airborne the target thus they have less control over their movement and the simulated trajectory of them is more accurate.