Heavy tank/tank/ifv/other combat movecraft should combat tag whoever got touched by the shell or other projectile's explosion radius to actually have an impact in a siege enviroment instead of having its damage patched up inmediately in front of said tank. It is a bit silly that you can just place more blocks that take several shells to break through again whilst standing where the tank is shelling effortlessly without any consequences. If you dont want the tank to start 1 tapping people then you should give it this ability instead than add more limitations on movecraft usefulness in CCNet.
You would still be able to spam fort cannons but would need to take cover first adding slightly more skill to it so there is nothing wrong with the suggestion really, atleast how I see it.