I think the best way to show an exact position would be a straight-on shot, a la the famous picture of Eddie Rickenbacker in his SPAD, or a shot or diagram from overhead. This third one still makes it look like the rear flexible gun's vertical post is touching, or practically, the fixed gun about midway down the barrel. The second photo clearly shows that the entire drum was forward of the post, which means the fixed gun had to be a foot or so to the right of it and much closer to the edge of the gunner's cockpit.
Did anyone else think the third picture looked like the gunner was getting sick?