At 20 yards the arrow will strike approx. 1.5" high, this coupled with a deer lowering itself during the shot can sometime make a difference. You surely do not want to over compensate and aim at the bottom of the deer but aiming at the lower lung area is a good idea. If you look at a lot of treestand shot deer you will notice that due to the factors listed above most are hit higher than the archer intended.
Good luck
BD