I think the difference in grain capacity is going to come from how thick/thin you mash more than the type of filtering item you have at the bottom.
I will add that I have a 10 gallon round cooler, and with appx 22 lbs of grain it it, it's pretty damn full. My grian bill is only that large when doing 10 gallons batches, but I am not able to batch sparge with one single water addition... I have to split the sparge water in half and do two smaller rinses.
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