Since I use a relatively low effective DPI, the calculated In-Game sensitivity went below the minimum of 0.5, which is too fast for my liking, which is why I tried setting the in-game sensitivity via the config ini files, and I think I found a way to accomplish that. While I don't know whether the conversion is an exact fit, it at least felt way better than just using the in-game minimum of 0.5.
Here is how I did it.
Open the following file:
%USERPROFILE%\AppData\Local\BPM\Saved\Config\WindowsNoEditor\Input.ini
Edit the following lines:
AxisMappings=(AxisName="LookUp",Scale=-1.000000,Key=MouseY)
AxisMappings=(AxisName="Turn",Scale=1.000000,Key=MouseX)
Replace "Scale=-1.000000" and "Scale=1.000000" with the multiplier calculated by the tool. For example:
AxisMappings=(AxisName="LookUp",Scale=-0.300000,Key=MouseY)
AxisMappings=(AxisName="Turn",Scale=0.300000,Key=MouseX)
Since the tool doesn't calculate anything more precise, that's what I am using. While it may not be perfect, it's way better than the alternative. If the tool supports config file mode in the future, more precise sensitivity settings may be possible. Note that the in-game sensitivity slider needs to be set to 1.0 for this to correctly translate.