Playing Bronnox (the "Brit is suicidal" mission) now. I confirmed that the terrain concealment on Expert applies not only for mountains and hills, but also for other type of terrain, though to a lesser degree. I can't believe that I am opening up the fog of war so quickly on this completely flat stage! Since I am trained in other stages never to rely on seeing anything, and always maximize vision/radar coverage, this stage (at least the first two turns) feels really easy. I'll update on my progress during the weekends
By the way, one thing that I probably do differently from most other players is that I rarely use the buggy for its actual offensive capability. I use it strictly as a recon vehicle too. Stretching your precious recon capabilities is key...