I think too elements of Antietam's landscape/farm fields allowed for some protection. I also think Lee was banking on the advantage of George McClellan bringing himself to the battle as well.
That's a neat article Ned, thanks for sharing it! I'll have to watch his presentation later. I spend a lot of time at Antietam and down in the area of Burnside's Bridge, though not always at it. NPS has been redoing the landscape a bit in the area for almost two years now. Made an access ramp down to the bridge from the parking area at the top, which is roughly where Benning had his lines. The parking area I believe is slowly being moved to the backside of the hill and the walls & displays at the top of it are closed off and being removed. Though I haven't confirmed it 100%, I assume it is part land restoration, which if the case, I'm curious to see if research like this has any part of it. It also is an accessibility thing too. The ramp is a slow grade sidewalk that does down the side of the hill. I've got photos I can dig out and if I go to Antietam in the near future, I'll snap some more. It's been really neat to see the work unfold.