Good interesting read. There is some logic there but surely all they're saying (raceglaze seller) is the taller, the better. They're not considering water travels through all the resin and not just through the direct route bypassing the resin around the outside.
My logic is the more the resin, the more chance you have of removing impurities at a higher flow rate.
But, I look after new car engine projects for a living and not water purifiers so its highly probable i could be wrong.