Well I think that many times they don't have to look up to see you. From a small distance you are just in their natural vision range, as they get closer they may look up toanalyze what they saw from farther away (if lacking a secondary sensory verification). I spotted a hunter in a tree stand just tonight, I was glassing a back corner and saw a blob in a tree. Once I zoomed in sure enough a hunter, (obviously not wearing UC ).