My experiences don't necessarily show any clear-cut correlation between fly size and bass size.
When I first started flyfishing, I was primarily targeting bluegills and crappies in the local public ponds. Everything else, including bass, was welcome "by-catch".
I would catch decent numbers of bass while fishing for bluegills and crappies. I wouldn't catch many "big ones".
I arbitrarily selected 18" as my personal definition of "big bass"...but even the 15"-18" range bass are good solid fish in central Iowa. In my own opinion, bass in the 13"-15" range are when they transition to having a big enough mouth and body to effectively eat large prey items (like 6"+ bluegills) on a regular basis.
Several years ago, I started actually flyfishing for bass using poppers that were too large for bluegills to eat. My catch rate on larger bass went up by a very noticeable margin.
After a couple years, I stepped up to an even larger blockhead popper design. The bigger bass LOVED that, and still do (although the local bass seem to be getting wise since I use it so much). My catch rates of the 18"+ bass climbed higher. It has held pretty steady over the last 3 years.
I've also started using larger subsurface flies for bass....shad imitations, bluegill imitations, attractors.... flies that I often tie in the 3"-4" length range. Bass have been liking these as well.
|Bass on a 4" Gamechanger. It could have easily eaten a much bigger fly!|
|Bass on a Blockhead Popper. Looks pretty small compared to the fish!|
But during this same time, I've had times when I couldn't catch bass on the bigger flies, switched to smaller flies to target bluegills and crappies...and THEN started catching nice bass on these much smaller flies. Also, one day I was casting shad imitations because the bass were chasing shad. I caught plenty of 14"-16" bass. I switched to a smaller dark fly, and started catching 17" bass in the same areas I'd been fishing previously.
|Bass on a #6 DDH Leech|
|Bass on a #8 beadhead bugger.|
Or how about the multiple times I've caught 20"+ bass on tiny microjigs while flyfishing for bluegills/crappies?
|Bass on a 1/80th oz microjig.|
What is the verdict?
Regarding small flies:
I think some people catch big bass on small flies simply because that is what they are using. Or maybe they are fishing water that gets high pressure from bass anglers using the typical larger lures spinning and baitcaster anglers cast for bass...and the bass have learned to not strike those larger items in the water?
Or maybe there is a hatch going on, and/or the bass are focused on a certain type of easy meal at the moment....such as dragonfly/mayfly nymphs, leeches, or tiny minnows.
In other words...put a small fly in front of enough big bass, and eventually one will probably hit it. Its very likely you will catch many smaller fish in between the bigger fish.
Regarding large flies:
And fly anglers tossing huge flies for pike and muskies will often catch large bass on those giant flies. Big bass will definitley hit big flies. Maybe not all the time. And a bigger fly might keep smaller fish off your line long enough for a big bass to eat it.
In other words, if you are after big bass, toss big flies. Eventually you'll catch big bass if they are present. Don't expect to catch many smaller fish in between the bigger fish.
Final answer: There is no right answer. Fish whatever fly sizes make you happy, and that you have the most confidence in. If they are present in the water you are fishing, eventually you'll catch a big bass. 😎
Using smaller flies probably requires more skill in hooking/fighting/landing fish because of the smaller hook. In my experience, a bass will shake a larger hook less frequently than a bigger hook, but neither has a 100% success rate.
Your best bet? Have some big flies and small flies with you....let the bass tell you what they want.