My GA opponent set only 2 of the 3 defensive slots available in each 3v3 territory. While it's possible they did this intentionally, or because they didn't have enough squads, it seems very likely that they just didn't notice there was an extra slot available: there are only two glowing circles which represent a squad in each territory that get animated with the leader toon, so it would be an easy mistake to make. Might reconsider that design element.