No I figured it out, I was measuring correctly, but there is something inconsistent about the slider in game.
According to the calculator 3 in game sens, 700 DPI and 109 FOV should give me 20.2 inches 360 distance. I was getting around 22 inches or so. When I changed from 3 in game sens to a different sens and exited the menu, then changed back to 3 in game sens I was getting the 20.2 360 distance.
The strange thing is that when I repeated the process sometimes I would get the "correct sens" and sometimes I would get the 22ish sens. Just plain weird, but Tiny Tina's does have janky M&K support.
I know that may sound like I'm just measuring inconsistently or something like you suggested, but I've matched my sens for dozens of FPS games I promise that isn't the issue.