Adding 2 washers got him back to the stock 9 lbs of boost. Adding washers is like tightening up the wastegate on say a garret turbo, each turn was about a pound of boost, but because the ECU controls the boost cut if you set it up much more that the tune is set for you could likely hit the boost cut. The boost cut is there for safety. When you hit the boost cut, the machine will shut off and come back on once the boost get back under that boost cut. Most all the tunes are designed for 9 lbs. of wastegate crack pressure unless you have the bigger wastegate.
He did this as his tunes were down on boost.