Before replacing new filters, how did you get the dirt out of the bottom.
All this dirt would be on the fan side of the evap, thus there should be little or no dirt in the evap.
However:the best way to clean it well is to remove the evap cover, and get in there with compressed air, lots of water and a thin brush. Check all the time that the drain is flowing freely. I take full credit for being the OP that pioneered this mod, BTW. One of the proudest moments of my life....