Ivanoff Style underwater corrector port on a Canon Marelux MX-R6II

Hi, I am looking for knowledge exchange and more experimental tipps running an underwater corrector port Ivanoff style that I have been testing & shooting since yesterday on my Marelux MX-R6II.

Mine was not made by the famous Carl Zeiss, though. I think it was designed by fathom optics in the USA around the year 2000 for video shooters.

I was hoping to shoot a flexible 24-70mm or 28-70mm behind it, but failed. MFD of the lens utilized behind it seems crucial as with dome ports. The Canon RF 28-70 and 24-70 options have really bad MFD, even worse than the RF 24-50.

The Canon RF 15-30mm IS STM seems run awesome behind the optic. It is severly larger than the Carl Zeiss underwater corrector port that @Alex_Mustard has used before.

The cheap Canon RF24-50mm which is said to run nicely behind a WWL-1C(?) has turned into a complete failure behind that water contact optic. It just cannot focus once you zoom in and it fails to focus on land through the optic. I think it‘s due to the bad MFD of that lens.

However I have some flexibility concerning the amount of extension rings I can put in between and I would like to nail the best focal point possible behind the curved inner sphere.

If some of you have links to scientific papers or schematic drawings of Ivanoff style optics I would be very thankful if you could share them with me.

Edited 5 hours ago5 hr by Adventurer
added some images of the construct