[Imp]

Up to 10 hexes is quite reasonable full moon or city lights in the background, no moon middle of nowhere so no man made light for miles try you might be aware somethings there at 10' but no idea what it is. If it moves then can detect further out & your brain can guess what it is from cues how it moves sound etc & fill in the blanks. Modeling night combat well would be very hard apart from IR rounds muzzle flashes will make you visible at greater range or at least give a good idea of local. Tank firing its maingun will illuminate the area around it suddenly exposing anyone nearby etc etc.
As suggested lowering search a bit seems to work well having little effect on vehicle detection but making finding troops harder.
Night attacks are tricky things I think following terrain features is bad cause can silohette you but if dont use them many units got lost & ended up attacking somewhere quite diffrent to the intended target I believe.