What Buddy said I think is the most relevant. The thing with bass flys are that most of them are less aerodynamic and harder to cast. One of my favs is a muddler down to size #12. You'll catch bass, bluegill, pretty much everything on that size fly, plus they're easy to cast. The bigger the fly size the bigger the fish that can eat it. So by downsizing the hook you allow for more opportunities to catch fish.