The Wars of Reaving Supplemental p. 2 states that they Trey was the smallest formation independently deployed on combat missions by the Society (excepting irregular missions such as assassinations and the like). This would, in theory put them in the same position as a lance or Star for the purposes of the force/unit movement and construction rules presented in Alpha Strike, BattleForce, and several other publications. In that case, though, there's the problem that deploying a full Sept means the command Un is on its own outside of a unit/sub-force.
For the purposes of Lance/Star Movement, force construction, BattleForce unit construction, and other similar rules, what is the equivalent organizational unit for the lance or Star? If the answer is the Trey, is there a general rule of thumb to follow regarding the command Un of a Sept?