It is possible that aiming for a foot / elbow, or the top of the head, etc, can get a clear line of sight, when most of the target is blocked. Since the line of sight is calculated from the middle (IIRC) of the model, it is also possible that the middle of one NPC has a line of sight to some part of a character, but the middle of that character does not have line of sight to any of the NPC (depending on positioning).
On one of my tries, i was engulfing my own party in smoke. They still shot at me.
