You make an interesting point.. not having the gasket should only reduce the total volume of gas in the bowl by a small amount. But if the clearances in the float bowl are tight enough (since the carb is so small), having the bowl screwed on too far might be able to interfere with the float. I hadn't even considered that.
How thick is the gasket, when new? I've never had to replace one of mine, but I would assume it's in the 1-2mm area.