You're mixing up surface filtration and depth filtration. "Channeling" refers to the liquid passing through a bed of contaminates on top of a membrane in surface filtration, like a Racor. That bed of contaminates actually helps the filtering, acting as a filter media of it's own. When it channels, the liquid bypasses the filter cake and goes right to the media. Picture a nice, even coating of contaminates on the filter, then you scratch away a part to expose the clean filter media. That's the "channel".
However, in a depth filter, the entire length of the paper towel acts as a filter media. The "stuff" gets caught at one end, and the fuel passes through a LOT of filter media, both paper and "caught" contaminates. As long as your paper filter media is tight enough in the holder, it won't really "channel". Now if you put a roll that's too small in there, it can bypass it, but that's your bad, not the filter's. It can catch lots more than any surface filter...that's what makes it so good for polishing applications.