There seems to be a real tendancy especially for trad archers to shoot (not aim) high on animals from tree stands. It is critical to keep that basic "t" form (torso and arms). Do this be either dropping a knee (Byron suggests this to keep your body weight centered), or bending at the waist. Schulz also suggests canting the bow more. In any case as already mentioned, you need to practice in the same type of scenerios that you expect to face.