YB beat me to it. I also have a horse who like to fall through the right shoulder, and the fact that I like to tip over the left shoulder doesn’t help! We do a LOT of moving back between correct bend and counter bend on circles and figure-8s. The point is that he doesn’t know which way to bend (or whether to remain straight and true) until I tell him. He’s the kind of horse that likes to assume control and I always have to be a little bit ahead of him.
Your horse has figured out a resistance that works. You just need to change up the game plan and get him to respect your leg.