NoCams is correct, bending at the waist is the best method. I have another idea to add, when shooting at game from an elevated position, you will see far more of the other side of the animal, in other words you see the spine, and the off side.
This can make the target area appear to be wider than it really is. Most people will not focus on the side nearest to them, and not pick the spot. Couple this with a tendency to shoot way to fast and you have the high arrow syndrone.
In addition to bending at the waist, I have begun to make my self hold after I find the spot I intend to hit, an extra count and one half. My high shots have almost completely disappeared.
Barry Wensel once said, "when you encounter game, and the shot is rushed, the tendency is to shoot high'.
I think Mr. Wensel is right on target with that. I might suggest more practice at the height you will be hunting. I find the more I practice from an elevated position, the more confidence I have, and the less likely my shots to go astray.
Seems like everytime I think I have figured this game out, some stupid deer comes by and makes a ass out of me.....I hope your next shot will be spot on!