Very interesting, and complex!

What I read about conical headers is that, with the small opening in the gas intake, and a larger one at its other end(to the pipe), the gas flow gets accelerated(SP?). That is because pressure difference, if I remember right. The smaller part have more pressure than the larger one, so the gas flows "accelerated" from the high pressure zone to the lower one, to attain equalization with the atmospheric pressure as fast as it can.
Thats why the scavenging process is better on the conical header, it sucks more gas from the chamber, thus getting more fuel on it, faster. Thats also why it will, on a direct with a standard header(consider variables equal, temp, pipe ...) consume more fuel, its getting more fuel into the pipe also.
Thats right ?

(I am very bad with writing too, and that in my mother language, in English then ...)