Channeling can ALSO result from an oversized pump.

You have to understand, pool dealers want to sell pools, more than they want to sell pools that work. American customers tend to be much more impressed by "MORE HORSEPOWER" than they are by "BIGGER FILTER"! Plus it's cheaper to 'upgrade' to a 1.5HP pump from a 3/4 HP pump, than it is to upgrade from an 18" filter to a 24" filter.