The best way to kill someone with a 2 inch mortar is to beat him over the head with the tube. "Sights" are a white line down the side of the tube. We had better uses for the 2 men elsewhere in the platoon as riflemen or runners etc.
That being said - the first Tiger 2 kill in Normandy was with a 2 inch (parked, bombing up beside an ammo truck which the tiddly little bomb set off)
Cheers
Andy