Your whole dynamic changes if your are lowing your arm instead of bending at the waist -- think about it, when standing, everything aligns generally parallel to the position of your hips and feet (and your "gun/target" line -- the path that your arrow will travel from bow to target). By lowering your arm instead of bending, you throw that alignment off and your point of impact will change. The key to shooting anything consistently is to do the exact same thing the exact same way every time.

Try it -- if you practice from your treestand and are not bending at the waist, you will find that you still shoot consistent groups, anywhere from 4" to 12" high.