One thing that I've noticed is when you send in men into a building, they wait until the movement of most if not all are complete. During this time they're awareness is low. So when I send them into a room with surpressed ememy, the ememy sometimes recovers before my men attack them (even when using assault). The way I get around this is to wait until 3 or 4 enter the room then cancel the movement order. Then they become "aware" of the enemy faster. You've just got recognize that half of the squad is now outside, and probably exposed. Use this tactic with care + planning.