Refillable Coffee Filters Let Through Grains Into the Coffee Cup

The sediments and grits that you feel at the bottom of the last cups of coffee is something that is because of the permanent filter and not necessarily related to the grind level. You'll get that "sludge" in your cup basically with all grinds, but expect more with a fine grind because more particles are apt to slide their way through the filter.

But with the reusable filters you likewise enjoy better coffee because they don't absorb as much of the aromatic oils of the coffee grounds and they let them through into your coffee so you can enjoys more richness of the coffee bean flavors that would be caught up by the paper filters and you'll also avoid the paper aftertastes of disposable filters, although the paper filters do give you a cleaner cup of coffee holding back the coffee grains from getting into the coffee.

My two cents. Hope it helps.