I have found that as long as the deer is upwind and you can stay still at critical moments, then height isn't much of a factor. I have stood face to face with a nine point buck, 5 feet from me, as long as no movement is detected, and he can't smell you, he or she will go back to whatever they were doing.
I must mention that if the deer senses something is wrong, it will stomp its front feet at you. You mustn't even bat an eyelid, when this happens, or your chance at a shot will be lost.
Hope this helps.