Just did mine on a 2013 Cartels few hours ago!!!
I was able to get the back side (-15) perfectly lined and parallel with the board edge. The front however (+21) , just slightly off!
I know your issue EXACTLY! That's what happened on my old P1.1. But with the new 2013 Cartels what I did was un-screw the outside 1st, rotate that side and tighten. Then move on to the outside screw, undo, rotate, then tighten. It sat over the heel cup PERFECT (to my surprise cause that was always an issue). Once done that, I did my +/- forward lean.
I hope this helps.
err which one, outaside or inside, should be the first to adjust??