I have figured out the problem. Using MouseTester, I have measured a more accurate DPI measurement of my mouse. It turns out my mouse is using 900 DPI for some reason even though it is set to 800 in the software. If I substitute 900 instead of 800 with your calculations, then I receive 35.433070866141732283464566929134px/mm. And now the sensitivity matches up. Thank you for doing your own tests, as it showed that something was wrong with my mouse.