So, my understanding on reading Firefight is that a single unit can only take and hold one position and that any descriptions to the contrary are just color.
If a map has 5 positions on it, for example, and there’s 2 units in the Firefight, 3 of those positions will always be unoccupied.
Also, at the beginning of the fight, unless the winner of the Contact roll chose to use it to occupy a Position, all five would be unoccupied. It’s also quite possible in the course of the fight that no one ever occupies a position.