The tensioner does not do all the work, look at the timing belt VFAQ diagram to understand. You have to set the tension manually using the eccentric pulley, and the tensioner is there to take up slack when the car is revving.

Brothers, next time there is a real easy test to see if the tension is correct. When you set the tension and let everything settle, see if there is any resistance in the tensioner pin. If there is any resistance the tension is wrong (and by looking at the tensioner shaft position relative to the pin hole you can tell if its too loose or tight). If the pin slides freely, you are good to go.