The pinch test as it's known is an excellent way to adjust the low speed needle. However, the main needle is best set as RCKen and a couple others suggested.

The needle really needs to be set for flight, and all the ground tricks fall short of predicting what mixture is going to work best with your engine, turning your prop, on your airplane once the airplane is in the air. Richening up 2-4 clicks from the peak ground rpm is absolutely good enough to get the airplane in the air with a safe initial setting that you can then judge IN THE AIR. All the tricks including the 2-4 clicks richer, really aren't the end of the process. How the plane flies after it's at altitude and your heartbeat is back to normal is what you THEN judge.

Bottom line is to get the plane in the air with what should be a safe needle setting and then see how the engine is running. You'll see experienced flyers maiden models and set 'em back down after a lap or two, adjust the needle a click or two, and go right back up. They're doing what you need to be prepared to do, set it by how it works after all the cute tricks have been done on the ground.