Nice!
So first of all, remove everything from %LOCALAPPDATA%\TslGame\Saved\Config\WindowsNoEditor\Input.ini. This fix actually still works, but it is added to the new setting.
If you set the new parameter in-game, set Vertical Sensitivity Multiplier to 1.43.
If you do it in the config file, set MouseVerticalSensitivityMultiplier=1.428571.