which waters are you talking about and what exactly do you mean by tiny impressionistic vs large realistic? I certainly will throw the biggest fly I can but often times tiny means realistic. This time of year its midges and more midges and Im sure you know natural midges don't get much bigger then a 20 and thats even pushing it. Ive heald a 22 RS2 that I was fishing as a sunken adult midge next to a natural and my fly looked like a gorrilla compared to it. Still, Im not about to go to a 24. I might get a couple more hits with it but I will cetainly get a "swing and a miss" type day with a 24. Bottom line though, I think you can go pretty tiny and still be realistic. I tie a fly called a UV midge that is a great go to fly when midges are out. If you want this pattern let me know.