You do not want to use a twisted snaffle. That is going to do nothing to help you or your horse. The answer is not in a harsher bit which is what a twisted snaffle is. Just work on your transitions and working on moving your horse in working his back end into his front end. That only is what is going to allow him to move properly throughout his whole body and rounding properly. Rounding is not just in the head and neck. It is in his back his legs and bringing his butt up under himself and working properly. There is no quick fix nor is it going to happen overnight. Keep working with him in transitions serpentines, circles, bending, trotting poles. But do not switch his bit it will do you no good.