By design? Gunner mortar fires from his feet

The way the gunner mortar fires makes it really hard to use sometimes. When firing it down from a ledge, you have to be right at the edge or the shots will just hit the floor at your feet. If there is a lip at the edge, forget about it! You also can't really fire it through openings like some of the walls have on top of laserazor arena

Yes, I've noticed this on close range hits... you totally have to expose yourself if on a walk-way, you cannot arch over the edge. You literally have to stand on the edge for your shot to go over..

It is indeed by design.