FWIW, if you are 10 yards up(30 feet) and the distance from you to the deer is 20 yards(60 feet) then the distance from the base of the tree to the deer is 17.32 yards(51.96 feet). A difference of 2.68 yards(8.04 feet). At 20 feet up things look a lot better for shot angles at closer ranges....just something to think about.