For Horse and Musket, some rules will say that their melee / close combat is not actually representing man-on-man / bayonet type fighting, but rather is a generalisation to represent the CLOSING of one side against the other, the last 100 yards thing and that it is the PRESENCE of one side prevailing over the other that is actually occurring, so one side may be giving way, by falling back, before a mass contact takes place - in those circumstances, a ‘falling back’ seems perfectly natural and is just some fancy footwork that is matching the attackers approach.