Unfortunately, the straight down (or nearly so) from behind shot is a bad one with a bow (live and learn). It's one of those hard life lessons that you should wait for the shot when a deer walks up from behind you and underneath your stand. I have let several pass that never did offer a broadside or quartering in shot since my lost buck. That was the first year I had hunted from a tree-stand and, as I said, I went back to still-hunting for many years after that.
I only put one up again four years ago after we purchased a home with land.