It's the positioning of the body. The neck is fine. But the body is way too far to the right of my body, so it's like I'm picking way over to the side, not in front of me.

I've used classical positioning before, but it's difficult to play for several hours like that. I tend to get sore.

Jest, are you saying you play with a strap sitting down? If so, you must have it really tight for it to have any effect.