How to choose a mid-range lens for Canon system （dome port）

Hello everyone, I previously used EVA Marine soft waterproof shell with RF24-70 in freshwater underwater photography. Although the edge image quality is poor, it can obtain some behavioral photos of sensitive organisms. Also, my luggage allowance is very tight, and it's a bit difficult to carry the flat mirror port

I am looking for a medium focal length lens (50-85mm) that can be used behind a spherical mirror (140mm) on the Canon system with my fisheye lens. Currently, the closest focusing distance of Canon's RF50 1.8 and RF85 f2 exceeds 0.3m, and theoretical calculations show that they are difficult to focus with the 140dome without using an extension ring. If combined with a 30mm extension ring, I can‘’t be sure if better image quality can be achieved because there is no parameter for the entrance pupil distance for rf 50 and 85.

Regarding other zoom lenses for RF, it is more difficult to meet the entrance pupil distance as the closest focusing distance is bigger.

Do you have any good recommendations or experience sharing？ Thank you