To be counted towards skirmishing the Units must be within 450 yards of the enemy, which in most cases means that if the footprint of your Units is similar to that outlined in the Introduction then you’d get a max of four waves skirmishing against a target Formation, assuming they were all base to base and the Formation was right up against the enemy. In most cases I would guess you’ll only get two or so waves but as to the rules, it is simply based on distance to the target Formation.