I was just curious, I am a beginner and really fight hard to keep shoulders aligned with board. I currently ride +15, -6. I learned to ride from snowwolf videos on this site. I have to put my right arm behind my back to keep me from wanting to counter rotate. I didnt know if I changed my angle forward if I would not have to worry about my shoulders. I ride pretty well for an old guy so I wont mess with it.
Like Cifex said, the angle, even 18 (which is huge for a board) won't make you face forward any more than usual. Think of using your shoulder or lead hip to point where you're going and follow that. You can also look over your shoulder (while it's pointed straight down the mountain) like the sight of a gun to help keep your upper body aligned.
You square your body to your feet, so yes, you'll face more forward. My angles are 59/58, so I have a fairly forward facing stance. "Squaring up to the board edge" is just a result of common angles that square or duck the feet evenly across the board, and not the other way around.