OK. 30% would seem to be the minimum moon illumination for a good effect. Note that this has nothing to do with the mod! Even on zero illum the buildings, vehicles etc are perfect. Just the ground textures seem to blackout. In Helos you can use the Search light to good effect well before you can see the visible light, which is realistic - just pretend it is an IR search light
Gamma only enhanced the issue, same as gain.
The app mentioned above works really well. I would recommend minimum 30% illumination and remember that cloudy skies will make a big difference too. Training? 30% and clear skies. Good luck and keep that head moving