FOV question RE two wwl water contact lenses

This is just idle curiosity, I suppose, but many of you are much more technically adept than am I. So maybe someone can explain:

I happened to notice that a Nauticam wwl-c on a Nikkor 24-50 lens has a converted field of view of 130 to 81 degrees. The wwl-1 with the same lens and camera has a converted FOV of 130-72. I would have thought that any difference might have been on the wide end since with the wwl-c, the lens can be used at 24mm while on the wwl-1, the soom range should be limited to 28mm on the wide end.

I am guessing it is just a result of the optical construction, but it confounds me. Perhaps the optical design accentuates the wide end (to allow 24mm) and that resulted in a reduction in the effects at the long end?

If this is a technically stupid question, please be gentle.