The bigger the body of water you fish the bigger the fish,Blues and flatties can get about the same size most of the time.But i have seen in books of blues that were caught befor the civil war being 300+ pounds.Bue i would recomend useing live bait for flatties find log jams with deep holes around them during the day.LIve blue gills and live eels, our state record was caught a couple sundays ago here in NC off of live eel it was 78 pounds and 52 inches long in the same river i do all my fishing in.Also flatties will move to shallower water at night to feed on bait fish. I would find out what fish are in the waters you are fishing and any of those can be used to catch faltties even small catfish.