I think the relationships drimzi's formed/come upon between FOVs with diagonal 1:1 MM is worth looking into.
I tried matching sensitivities with viewspeeds V1 and V2 quite a bit before coming to this thread and seeing new ideas. Between those two, the other trial solutions drimzi posed, and diagonal 1:1 match, the latter's transitions between different FOVs felt more "right" to me with than with any previous, did so basically immediately, and still did after going back and trying other solutions again. I think it got generally good reception from others too, so I'm interested in what you think about it, if you're planning on trying it out.
I don't keep up with the math going into this beyond basic concepts and goals, so I can't attest to how sound anything is, or explain why 1:1 diagonal match feels so good to me. However, a lot of this has basically been trying out different ideas to see how the relationships they produce feel. Considering that, I wouldn't be surprised if diagonal match wasn't the "right" solution, however even an incorrect solution that grants insight is a step forward that can be important in finding better ones.
To me, a mathematically-based solution is preferable, but only if it produces preferable results. If it's beat out by something that isn't as nice and transparent of a solution, figuring out why that happened and using that new understanding to craft more grounded solutions is the next step, right? That's my take on this, anyway.
Of course, this only applies if other people are as into the way diagonal 1:1 monitor match feels between fovs as i am. If not, then it's not worth worrying about.