When I was a senior in high school (and still shot a wheelie bow), I had a problem with my scholder dislocating and the doc said not to do any pulling/pushing over my head (e.g. climbing trees), so I was confined to the ground that season. I ended up shooting what is still my largest buck that year at 8 yards. Since then, I've killed a few more off the ground, but they've been in the 15 - 20 yard range.
I think it's more important to have good cover behind you compared to infront of you to break up your outline. For that buck at 8 yards, I was standing infront of a huge oak tree. For others, I was sitting infront of a patch of thick grape vines.