Meant to post this a while ago, but it seems like ultrawide resolutions (really wide ones) affect the sensitivity??! Or let me rephrase that, it seems like MWR doesn't really support ultrawide formats wider than 21:9 (not so sure that's the exact cutoff or even if 21:9 is "properly supported"), and that seems to affect the sensitivity somehow.
Here is what I'm rocking with, and you can tell something isn't right (sensitivity wise), even more so with what I would actually like to use. The latter is wayyyy off, and not quite super ultrawide for whatever reason. Images for reference:
So yeah, really weird behavior, guess there is a reason why people call MWR a bad port. Something similar I have experienced and is actually worth looking into (calculator wise) is in CoD2, when you apply the ultrawide or multimonitor fix, it also seems to affect the sensitivity, but in this case, ultrawide formats wider than 21:9 work just fine.