As in real life forest, canyons, water can affect communication nowadays let alone with the equipment in World War 2. As a rule of thumb if you have LOS you should have radio communication. Even cell phones work because of cell phone tower antennas. Tanks and Infantry have a different C3 structure in the game. I noticed C3 is often broken when the command units with radio are traveling. Watching an old WW 2 documentary they their command post up in an old factory on top of a hill with a tremendous line of sight.