Even if you somehow manage to strike the coords, the shells are completely useless. They don't hurt T1 castes (except runners but good luck hitting them) to force them retreat and rest. Recently, during a Solaris round, I literally witnessed a Sentinel get hit by 2 Incendiary shells (one of them landed 3 tiles away from it) but it somehow survived. I even saw a Hivelord walk off from a direct hit of HE shell like nothing happened. At this moment, using Mortar has no advantage other than maybe using Incendiary shells to deny areas for aliens to pass but most of the aliens already ignore green fire.