If you are talking about the automatic control dial on the bag door, that isnt about airflow. All that dial does is control how full the bag gets before it shuts off and pops open. The suction/airflow is going to be the same no matter where you set the dial. If it has the blue lines in the dial, the closer you dial to one bar or none the sooner it pops open. The more lines on the dial the longer it runs without popping open. Later luxes have numbers instead of just lines. 1 opening soonest and 4 or 5 going the longest. I set my 1205 about in the middle, but I dont wait for it to pop open anyway. The 1205 is one of my favorites but its not the greatest suction to start with anyway. I hope this answered your question.
Control if low bag pops open soon. If HIGH you get more Stuf
That "setting" really sets the spring level that is used to determine when the pressure drop across the filter is "too high"; ie when the door pops open.
There are two pressure taps that are "looked at"; ie sampled.
One is a static port right past the Hoses bayonet.
The other static port is behind the filter, ie the part one handles ie the outside of the filter when it is in the vacuum's chamber where the filter goes.
These two static pressures go to either side of a diaphragm device inside the door of the vac.
When you turn the "adjust" dial; it pushes on an lazy weak coil spring that touches the diaphragm. This changes the pressure difference required to open up the vacs door; and declare your bag is full.
The Control if LOW bag pops open soon with not much filling of the bag. If HIGH you get more crud in the bag, but less suction towards the end, plus more crud passing through the bags if they are poor.