First off, while I haven't done any calculations to verify it, I have an intuitive feeling that an airbox designed to specifically reduce noise, may not resonate at the right frequency for optimum engine operation.
Also, if the engine is designed as a complete system, there is no reason that this "midrange dip" he talks about can't be exactly at midrange. If all this is correct, the end result would be that redline or peak power, whichever they feel is best, should occure on the harmonic of the airbox, so you would get another boost running WFO. Even better, would be to design the airbox for top speed and tune for this "midrange dip" to be on the harmonic.
In the days when air filters were just large air strainers that were often not even used, there was no "midrange dip" in power and torque curves, which makes me think that airbox design is mostly sound damping and the resonance is selected to minimise their detrimental effect on engine tuning where the designer feels it is most needed.
The dyno charts I have seen for Freak equipped bikes do indeed show a bit of a negative spike in the power curves around 3000 - 3800 rpm's, but those seem to be cleared up by carefull carburettor tuning.
