nybowhunter hit it right on the head. In high pressure areas the deer will look up. I have been picked off without movement at 15ft. If you can get on a knoll then 15 ft should be ok. If not then go 20ft+. If you stay 20ft above the line of sight on deer then you stand a much better chance of not getting seen. If you are uncomfortable with these heights then look for the high ground with sign and set up in your comfort zone. I have seen a dramatic improvement going higher.