No you don’t get it.
Set up single server queue.
POS assign one minute. Gantry passes are soap, wash, wax, and rinse and takes four minutes. Customer drives out of wash bay and has one minute to drive through a free standing dryer that’s positioned 15’ beyond end wall.
So, service rate is six minutes or 10 cars per hour and the most you can have in the system at one time is three cars.
If customer pulls away from dryer prematurely, how does this improve hourly capacity or increase number of cars in system?
It doesn’t. Only change is it doesn’t take as long for this particular customer because they chose not to use up all of their time drying
The only way the next customer can save any time is to not dry their car.
I’ll argue this all day because you are wrong. If you want, I’ll give you some queuing models in excel to prove my point.