That's a good question, Joe, and I do agree with Byron (who is being overly modest with his skill). My needs haven't pushed me to be a comfortable tyer of tiny bugs. Given your location relative to the San Juan and Colorado waters, I understand your interest in smaller patterns.
As a caddis, I'd rarely have a use for the E/C below #16,...and never below #18. I tried tying the E/C in a smaller black midge version with a poly wing subbed and wasn't pleased. I do like tying with poly in some applications, but it doesn't give that feedback that the right clump of good hair gives when I cinch it down.
Here's a BWO tilt wing dun on a #20 with a deer wing and split tails. As small as I care to go in this style.