Alot of good suggestions here-
I would suggest since your shooting error is vertical, that any thing you can do to get your eye closer to the level of the target is going to help.- Bend your knees, squat,whatever. It will reduce the amount of calculations that your subconscienous mind has to make at incredible speed to send the correct instructions to your body so that it can make the right moves to make the shot. Anything you can do to reduce the amount of calculations, will reduce the amt. of possibly incorrect or hazy info. your body reacts to, the better off you are going to be. Simply put, keep it as simple as possible, reduce angles _(both Horizontal and Vertical) when possible.
On another mental front, I have found, that when I have a bad shooting days (also bad golf days)its because I am trying to MAKE it HAPPEN, rather than LETTING it HAPPEN--if you get my drift-- We often get in the way of ourselves--relax, let your mind and body do its thing - its incredibly capable. Anyway, reduce angles where ever possible--Its a Good thing-can do you no Harm. Is this a GREAT sport or What!!!