It is the other way around for tuned pipes. Longer tuned pipes (the length is from the piston face to a point just past the mid length of the reverse cone) return the positive wave a bit later, which matches lower piston speeds. A shorter pipe returns the wave earlier (because the pipe is shorter and the wave has less distance to travel), which matches higher piston speeds. A fatter pipe theoretically produces more power, but for not as big of a window of RPM because the wave strength is strong, but has shorter duration. The opposite is theoretically true for smaller belly section diameters, longer duration of wave force, but less strength in the wave. For best pewrformance, the pipe needs to match the porting (and not many do). Here is an example

A g260 with one of the best pipes out there makes about 4.2hp

I know a guy who developed his own 25cc engine and machined them. He had a student of Dr. Gordon Blair (the grandfather of the modern two stroke IMO) develope a pipe to fit his porting. This was a piston port engine also. The result 7.2hp.