His rear arm, is under the armpit. It's not where it is in the diagram no, because it was hard to make a diagram that looked right with the arm as he has it. I'll have to make a video to show you guys how to do it. He doesn't change position, he stays in the same place with his rear arm in the same position. He's using the same technique in this video:
But it's easier to see. If you don't believe me, try it yourself.