Rule 465.2.c.3
Units must have lethal damage assigned to them in full before damage is assigned to a different Unit. Example: If a player has 5 damage to distribute among four 3 Might units, they may not choose to assign 2 damage to one of the units and 1 damage to each of the remaining 3. They must assign at least 3 damage to one, and the remaining 2 to another.