Nice shot Chris! I see in your photos that with the Subsee +10, you get a bit of vignette at upper right and lower right corner, when you hold it close to the port, the vignette is gone. So my workaround or mod will solve the problem. But then if you shoot video, which will extend the focal length a bit, the vignette would disappear. The vignette would show up in photo, but you can always crop away.
The ideal size I want to get down to is 3mm, so I ordered the CMC-1, but they're in back order now.