So I shot another 10-shot test group from my Ruger AR-556. Same setup as my earlier post:
Ruger AR-556, factory iron sights Federal American Eagle 55gr BT Caldwell bag front rest
This time I didn't use a rear bag, and instead pulled the rifle back into my shoulder using my left hand on the front of the magazine well. I also opted for a smaller black circle target, which I think helped me with holding elevation.
Here's some pics of the group, I think it's an improvement: