C · Positioning & configuration · §10
One body per battlefield, and the discipline to leave it there.
Enemy units at the battlefield do not matter. Friendly units elsewhere do not matter. Only another friendly unit in the same place, and the moment one arrives both of them lose the +2.
is in the list for exactly this. The first non-token unit played at it each turn lets that player move another of their units to base, which is a way to un-double a battlefield you doubled by accident. It is symmetrical, so read what it hands them before you use it.
does something similar on conquest: pay one, return a unit you control there to hand, and play a two-Might Sand Soldier token in its place. The token is a body that holds, and the returned unit is one you can place somewhere it will be alone.