I found that there is a 12 - 15 cup filter. Looking at the reviews for them it seems they all have had the same problem and the oversized filters took care of it.
My wife and I have Mr Coffee makers and have found we like to grind our own coffee and fill the filter as full as we can get it to get the rich strong coffee we like. Unfortunately I think the grounds float over the filter and drop into the pot. Is there a system we can use to get good strong...