Calculations – How to calculate the crop factor for the Focus Reducer for APSC in MFT?

I hope for a good / cheap focal length reducer, a cheap adapter, and sacrifice only the autofocus and save $$$ hundreds of dollars

What I'm trying for is the best focus reducer for my MFT-G9 camera (GH5-identical afaik).

What I do not understand is how big lens frames are scaled down for an MFT sensor because the crop factors do not match the ratios of the diagonals:

  • FF is 43.2666, APSC is 26.903, MFT is 22.5
  • Metabones XL 0.64x EF (not EF-S) to MFT
  • Metabones Ultra 0.71x EF-S (or EF but cut to size) on MFT

  • MFT diagonal / FF diagonal is only 0.52x, but I would expect ~ 0.64
  • MFT diagonal / APSC diagonal is only 0.83x, but I would expect ~ 0.71

Why do not my circumstances add up? How do you correctly calculate the crop factor for the focus reduction?