This is true for a multi-cylinder engine with a common intake manifold, where an "atmosphere" is created and where the pulse waves from the tuned runner length can work with. On a single cylinder engine like ours the runner is from the top of the restrictor to the crank valve, and the atmosphere plays its role as it is.

runner length ends where a sudden big change in cross sectional area is, and starts with the valve.

I would love to have your job that's got to be a daily school!

xe