I would guess that you are probably right and your scoliosis likely is the root of the problem. If you're right elbow is totally straight, your reach is definitely too long on that side. I'm not sure how you would fix it though. A piece of foam or cork under your bar tape might work but you'd still have to stretch to reach your brakes.

This is a very interesting question. I'm going to ponder it for awhile and I may come up with more later.