You are correct but I will note that the Sonex version uses a tapered needle in an orifice that allows more fuel to mix with more air as the slide opens & pulls the needle out of the orifice. Elementary in it's design it is said to work well for some once adjusted correctly. My experience with an early version wasn't comforting.Slide carbs are not metered by a Venturi. The slide opens up more metering holes the farther the slide is moved. Piccolo tube of sorts. It has to have a certain amount of head pressure or a pump or it does nothing.