What is your nock height? Are you shooting split or 3 under? Sometimes if the arrow is nocked too low, it will bounce off the shelf and impact too high.
Theoretically, if you bend at the waist and maintain the T shape of your arms and torso, you should be able to shoot from a stand without too much adjustment. Certainly something that takes some practice, though, and I wouldn't want my first shot from a stand to be at a deer. Even though I try to maintain a T, I still tend to hit a little high, so I hold a little low from a stand.