I've got a question on the KFL+ airflow screw. Should it actually ever get tight? If I start "tightening" it the airflow does go down and eventually stop all together. This I expected. But at this closed position the screw isn't actually tight. If I keep tightening the screw, the airflow starts opening up again. Is this normal? Or, should the screw actually be tight when it's in the fully closed position?