I think the type of setup needs to be taken into account. Tommy has a single stanchion with dual hoses, one for each side of the car and their sample states 14' centers. That setup has it equaly likely that the customer will fully open and vac from
doors on both sides.
At my locations the vacs are on an Island to one side of the vehicle. Customers spend little or no time taking the hose to the far side and vacuuming thru that
door.
So, along with space availability the type of setup is important.