Just tried this -- there is no auto adjust option in this mode. I think I read somewhere (in the manual or here) that this option is absent for DVI digital signals, at least at 1920x1080. Well, whether I read it or not it's true.
The vertical and horizontal offsets do work, it remains 1:1 but you can shift it around to center it a little better if you like. I left it at the default since it's too few missing pixels to really matter.