I am a relatively new hunter, and new to the saddle for the 2017-2018 season. I have been hunting this season between 25-30ft, and have had herds of deer feeding around my tree, where in prior years I would only see one or two in the entire season. While the leaves were on the trees, at that height, I never had a deer even look up. I don't choose a tree by diameter, but by location, so I have hunted large trees and narrow trees.
However, during the winter bow season, with all the leaves off the trees, (i) the woods are much quieter and any sound can alert the deer; (ii) even with a good back drop of other trees, concealment is much more difficult and (iii) even movement at 30ft can catch a deer's eye.
In these conditions, by way of example, a few weeks ago, I had seven antlerless deer feeding around my tree. It's really hard to avoid seven pairs of eyes when the trees are empty. A couple of the deer either heard me move as I shifted position or caught the movement, and looked right at me. As flinginairos said above, they just seemed to look through me without locking on to me, and went back to feeding. (I was wearing Sitka elevated II, but have had the same experience with a Mossy Oak kit as well.)
I doubt I will ever go back to tree stand hunting.