Good news! I'm old, blind and stupid!
Well, that's not good news, but the good news is I figured it out. There is a page in the Hansa C.I booklet that does indeed have pictures of the elevated gun ring experiments. I just figured out a way to miss it the first dozen times I looked.
So here are the different trials.
Steel tube tower.
Tower design apparently used by both UFAG and Phönix.
Tower with faired fabric extension. It turns out the idea was to create better airflow over the rudder. It was actually tried at the front and the book says the results were "unsatisfactory".
