Another thought, are the grips the same on the bows, for me if I place my hand on the grip to far to the right(right hander) that is closer to the center of the palm vs base of thumb, it will torque the arrow left. Different types of grips on bows may require slightly different hand positions to shoot well. So try putting the bow a little closer to the base of the thumb(moving your hand left), what have you got to loose. If its not that then my guess is the spine is the problem, closer to center shot needs a stiffer arrow, sometimes much stiffer.