I don't know if it can be seen or not - but I always "ground attack"-ed the houses where I last seen the MG. And I said I'm not a pro and just learning 1v1s. Why am I even answering?
No need to be a pro to see that the US mortar is bugged and fire at unit on the fog of war by itself, same if its target is moving far away from its last location.
Make a try, don't us it and see what happens.