Should I fix the limit and power to e.g. 2, or try to make them configurable? Fixing them is more user-friendly, but some might prefer to customize it, idk.
Also, what should we call it?
Legacy is a fixed conversion, either MDV 0% based on a FOV of 65 hdeg 4:3 (Legacy MW), or MDV 133.3333% based on your configured FOV (Legacy BO).
With relative, you can set the monitor matching distance yourself.
Not quite sure if there's anything else that affects it, but any item should say so. If you are unsure, just try to unequip your helmet and armor and see if the 360 distance is correct according to the calculation with 0% reduced speed.
63.6201% is correct because there's a bug in Apex where it rounds the 4:3 FOV to the nearest whole number before calculating the ADS sensitivity. So in your case, the FOV is 104.330730 hdeg 4:3, but the game rounds this to 104.
If you can attach here or PM me your config files I can take a closer look.
%USERPROFILE%\Documents\Call of Duty Modern Warfare\players\config.cfg
and
%USERPROFILE%\Documents\Call of Duty\playersBeta\[USER ID]\settings.2.local.iw9.txt
It does what it is supposed to do (MDV 0% based on a FOV of 65 hdeg 4:3), but being a beta there might be some optimization issues.
I can find anything out of the ordinary here though.
Just enter your current settings and select the correct games
https://www.mouse-sensitivity.com/?share=d733bf5c8af8d48cfdb91d14d410928a
Make sure to always check the game notes too, you have to either disable smoothing in GUNDAM or use a polling rate lower than 250 Hz.