ORIGINAL: 1QwkSport2.5r
I set my needle with the tank half full, starting rich and pinch the fuel line and lean the needle until I get no rise in rpm. This way when the tank is full, the engine will run a little rich and as the tank runs down it will lean out. If you pinch and the engine cuts out its too lean, if it rises it's rich. No change is peak or very close to it.
Running boats, you can see the fuel tank and can readily fill it half full to set up as you indicated. And then you get to fill it some more. The pinch test is helpfull in setting up a plane engine where the tank may not be visible. The pinch test is a very very simple and effective way to check that the engine is not set too lean.