During the game (insane no iron man) I found two situations, in which I constantly fail. I won't mention air combats, it's another topic and I can deal with them with just auto-resolve. But I just can't avoid clearing UFO.
The problem starts when I am starting my preparations to get inside, especially if it is impossible to leave heavy or sniper on a safe distance and blow the door, while your guys get closer with their shotguns (due to reaction modifiers heavy and snipers just can't shoot before enemy and die). When I move my soldiers to the door with enough points to fire with shotguns, some clever alien just open a door (I just wonder if there can be reaction fire on opening the door, because I like never had) and starts shooting aiming my heavy weapons guy and someone else, only after that reaction fire follows, and then his mates from behind add some more damage. Then inside there are more doors to screw my plans. Shield doesn't work, if you are scouting inside UFO - when you move into another room, some sneaky bastard shoot him from the side and you just can't prevent it anyhow.
So, guys, I would like to hear some piece of advice from you. What I do wrong? How do I clear UFO from those cheating campers?