I moved my soldiers to the concrete barrier in front of the building, but burst fire makes the concrete worthless. I don't understand how cover works, I thought I was under cover. I may try the mission again with tons of explosives and blow my way through to the leader. You can't use flashbangs unless you get close and probably breach the building on the side rather than the front, but then that will waste an extra turn or two and risk getting overwhelmed. Cleaners have good accuracy vs my green troops (3 missions at most). Grenades weight quite a bit too so you can't carry much. Even my shield guy barely has any weapons because the shield is so heavy even with warden armor.