In ww2 the range units (artillery, rocket, rrg) are covered with some units. But here in the game there's a bug where player can hit and run. My suggestion is what about range units can move after he attacked a troops but when attacking again he needs to reload first before attacking.

For short after range units attacks he can run away but when shooting once more he needs to reload bullets before it can shoot once again.

He can run away as far as he can but he needs to stop for some time to reload its bullet so he can attack once again