SPOTTING ANALYSIS
(I did these tests in Red Thunder which I assume has the same CMx2 game engine as CMBN and FI, and were done on Veteran difficulty level because that's the level Bfront recommend as having the best balance between realism and fun)
The main thing to remember is that even though many enemy units might be visible on screen,
only some of your units might be able to see them, so don't waste time screaming at the screen "WHY DON'T YOU BLOODY FIRE?"
1- The Germans are facing a Light Forest..
2- and in there I've placed this Russian 76mm ATG and a 2-man observer team. (Incidentally ATG's can't be placed in Heavy Forest)
Notice that the 3 German PzIV's are visible on screen (red circles).
Also notice that I haven't selected any of the Russian units yet, as the blank data panel at the bottom of the screen proves.
3- I now select the ATG and surprise surprise, 2 of the Pz IV's disappear because he can only see the one on the left!