If it's a WAR in question, Overpower is Conal as opposed to Circular, so they need to group the mobs up to be in the right spot (all in front of them). Also, I think it's easier on melee to have them all facing generally the same direction as opposed to all over the place. Not to mention being more grouped up is important for AoE's. To a SMN, most of this seems trivial as you mostly have strong, single-target attacks, except Shadow Flare which has a pretty big room for error. To a melee, however, having the mobs lined up a pattern helps a lot especially on MNK who's AoE hit in a straight line.