Any fly presented correctly will generally outfish a poorly presented perfect match to the hatch. BUT…a matched pattern, presented correctly will outfish them all.
That being said…give them what they want to eat. If there are sulfurs flying in my ears but they want black ants…then I fish black ants. 
Fact 1. Trout take emergers more often that true duns.
Ergo, surface footprint is not as important as fishing the correct stage of the hatch.
Fact 2. Trout have really poor vision compared to humans. We have 14 times the visual acuity of trout.
Ergo, surface footprint is not as important to them as it is to us because we can see more detail than they can.
Fact 3. Footprint is only element of what a trout sees not so well. Size and Shape are certainly more important most of the time.
Ergo, footprint is important only when the overall shape and size of the fly are equal between the two patterns.
Personally, I think footprint is way down the list in terms of fly selection.
I was under the impression that trout had much better vision (acuity?) than we did up close.
I was also under the impression that it was the footprint that the trout saw first when concentrating on taking adults. Next would be the wings until the adult came totally within the cone of vision.
However, given that no artificial fly floats on its tippy toes, maybe just a dimple, any dimple, is enough to get the trout interested.
… they’re looking for dimples ??
:roll: :lol: :evil: :shock: 
John
Thanks for that. I have read over 100 books on fly fishing and fly tying. One of them was devoted primarily to “What the trout sees”. It may have been by Clarke and Goddard - not sure. I know the limitations of a trout’s vision - particularly because they live in a mirrored surface which “disconnects” the insect’s body from its wing until the last moment.
I am also quite aware of the stages of insects in their life span. I fish a great many sparkle duns (the emergent phase - fully emerged, but not completely out of the shuck and wings dried off yet).
My search for a good footprint relates to the dun stage - when the fish are taking duns on the surface. It has nothing to do with nymphs or rising emergers (soft hackles/wet fies), or spinners.
On presentation: Good presentation is a prerequisite. It is NOT, however, enough by itself in all situations. In a hatch situation, the wrong fly, presented perfectly, will not in and of itself always be enough.
Thanks though
Byron Haugh
Here’s one I came up with a few years ago that I use for picky trout. As it fishes hook up it gets round the problem of the big lump of steel hanging down behind the fly. Otherwise it is really just a thorax tie.
Cheers,
A.
Interesting pattern
Well sure. But the Lochsa ain’t no over-fished spring creek. No carpet-thick mayfly hatches. And the fish there are more…real.
RE> Mike Lawson
…well. I never said spring creek and tail water fish aren’t selective. Royal Wulffs and Olive Drake imitations won’t work during a PMD hatch. But a wiiiiiiiiiiiide variety of #16-#20 olive/yellow wets and dries will work just fine. And what works best right now changes every 15 minutes or so.
Ask Mike about the “change patterns (to some other PMD pattern during a PMD hatch) if they refuse” concept. I’d be surprised if he didn’t concur. Every spring creek professional I’ve ever talked to works that way. Mike will be giving a tying seminar in Bozeman Jan 21st this month. I hope to be there. I’ll ask him then, if I get the chance.
Finally, on tail water rivers the “change pattern when they refuse” strategy doesn’t add up for float trips. At least not when fishing out of the moving boat. It does make sense when you are standing still or wading slowly and quietly, working repeatedly over the same regularly rising trout.
RE> the upside down dun
How often does that fly land and ride upright?
Since taking that photo I have modified it slightly. Using a piece of floss I split the wing post. That makes it land the right way up. If you make the wings out of CdC it is gives even better presentation. It rides OK., but the first ones I tied didn’t. I had used the Partridge K12 st hook (original Klinkhammer hook) but it is too long in the shank. I now use the K14ST (Oliver Edwards emerger) which is much shorter in the shank. That’s the one in the photo. You can also use the TMC 206BL if you want a barbless fly.
Cheers,
C.