I'll add also I think of about 20-50 yards as the red alert bust zone (from a tree). This is deeply empirical, and my logical attempt to explain it is due to angles and field of view.
They are close enough they are still extremely adept at picking up the slightest movement, but far enough they have a wider field of view.
50+ as long as you have any cover, you are usually ok with slight movements (normal treestand hunt scanning movement).
They get inside 20 and especially inside 10, depending on where the terrain guides the deers focus, you can sometimes do jumping jacks in the tree and not get busted.
How that plays out is when I'm looking at fine tuning setups down to the perfect tree, struggling a bit to put into words, but I try to avoid having deer hanging out in blind spots in the bust zone. And I try to set up my shots inside the bust zone. Really it's just stepping back and looking at where the deer's focus will naturally be directed by the terrain and try to steer clear of the worst of that.