It's been my experience that LMB will hit anything that even remotely looks alive.
Big fly...big bass makes sense...but more importantly big fly translates to big hook.
Bass flies in most cases have a single hook and you're more likely to land a 5 lber on a #2 and above vs a #4 and below.
Some pretty cool patterns posted on this thread and they'll all catch bass....but then so will an unpainted, undressed cork.
In my humble opinion, a variety of flies, that will cover top to bottom, is more important then pattern per se.
BTW...although a bass may hit a floating cigarette butt...it's not stupid enough to swallow it.