The simulation takes into account the size of the target, whether it is moving or staionary, visability, whether it is in defilade, target value, threat value and the ground the target is occupying..
It actually also takes into account the height of the vehicle doing the looking.
You can get a good idea what you will be able to see using the "LOS" tool. Just right-click on the unit and select "LOS". Sometimes terrain is not nearly as flat as it looks. Small, 5 meter ridges in the terrain may not show up on the map, but they are there, and will hide a vehicle (spoken from hard experience at the NTC).