Suppose we have a sandbox fight in which a number N pikemen supported by N ranged units face of against N infantry swordsmen supported by N ranged units of the same type that supports the pikemen. In this assumption the pikemen march to the swordsmen and fight in the middle while the ranged units do damage from behind. In my view, the fight would be balanced if the swordsmen die as fast as the pikemen do. In a simplistic model we could say that the damage the pikemen receives per second is