I got my 50mm f2.8 APO Rodagon-N today. I was able to get almost 100% framing with B+C+D, but I noticed the absolute corners of the 35mm frame had some light falloff.
I've swapped to using B+D+17675X with the 17675X closest to the camera, and the light falloff has disappeared. I seem to get light falloff whenever I use one of the original BEOON tubes closest to the camera.
Anyway, with B+D+17675X I am getting almost 100%, with just a little latitude left in terms of focusing, no light falloff, and finally I am happy. Expensive, though, but will last forever.