I've done some testing now to see exactly what's happening, and this is part a bug in the game and part mis-configuration.
The game maxes out at 105 no matter what you set in the config file and what is displayed in-game. So when you enter 106.990274 the calculations will be wrong since the actual FOV in the game is still 105. USA On will calculate the sensitivity based on what is actually applied in the game (i.e. 105), however USA Off will use the configured FOV (i.e. 106.990274) regardless of whether it is valid or not.
So in short, you need to use 105 as the game doesn't support any higher