I don't go by his site: MotoMan is obviously a zealot. Not that zealots must be wrong -- not so -- but if wrong they're generally blind to it and quite good at sounding as if their belief is the one true truth and just has GOT to follow out of logical necessity, and only conspiracies and stupid thinking can explain why just about everyone else says different. Hmmm, does that sound like MotoMan's site?
I've seen a small number of reports like yours saying the method worked for them, so that's a positive. I haven't seen anyone saying it failed for them, but that doesn't prove there aren't any.
An aspect to it is certainly true, which if he explains in exactly this way, I hadn't noticed on his site. Namely, that the kinetic energy of the moving air column in the intake tract is precisely proportional to the square of its velocity, or more precisely to the integration of the kinetic energies of each "slice" you could take of the intake tract accounting for the velocity at each point.
And, the work required to achieve greater than 100% volumetric efficiency -- to pressurize the cylinder above ambient -- is done by this energy.
Reducing the cross section of parts of the tract does increase this energy, so it stands to reason that there is a point where below this (narrower yet), added restriction from the narrowness exceeds the benefits from increased velocity, but above this, loss of velocity benefits exceeds reduction of restriction from increased cross sectional area. That point would represent the optimum -- either above this or below this would give less power.
Whether this optimum is at the size he says or not, I cannot say.
It would be interesting for someone else to do the work and try it on a ZX-12R head! :D