Also, units cannot change their deployment during the battle. How wide and deep you fight your HI is pretty dependent upon the enemy you face and how your battle plan. So unlike DBM, casualties are attritional. Units can be disordered by having friendly units rout through them or by entering nasty terrain. Disordered units fight with half dice, can't move and lose all combat bonuses.
Units also test when shot at.
A unit meleed in flank loses ALL combat capability. In effect, it is paralyzed and cannot defend itself at all even if also frontally attacked. In effect, it is dog meat unless a friendly unit rescues it.