Fix the problem where can grey zone camp in Monastary (Destruction) so that their tank is invincible

The defenders on Monastery (destruction) can par their tank near the monastery in the grey zone to that it cannot be seen or reached by the attacking team, but can shell the objective with impunity. I know this sort of thing is a serious is a problem on a lot of maps, but I wanted to call this one out in particular. Please fix it!