Yeah, I'm not positive on the whole neck angling either... so I could be wrong. haha. The heavy gauge strings and tuning down definitly could be part of the problem though. Since you do both I don't suggest that you straighten the neck out. You will need relief to play without buzz. The heavier the strings the more they vibrate... and the more they're tuned down the more they vibrate. So combining the two makes it that much harder to get low action. You will kind of have to sacrafice the action unless you can live with a little buzz. haha. A fret dressing might help out a little though.