The whole point of that basic RG series is to dominate the one arm (his right arm in the case of your left leg being used). So your focus needs to be on control on that side, which involves being on your right hip. If that control is very tight, you can use it to shift either his weight or yours to make the right leg more mobile. Otherwise, you will get the right leg over, but then wonder why he just slips out easily right away. It's because your don't have his right side dominated. Emphasize and tighten your left leg's control, and use that to get the right leg where your need it.