Thank you, SC. It is much as I suspected. I have read your post on selectivity, it too is an excellent post. Collectively your posts on the various BB would make a nice book, imo.
My thoughts run, that the eye of a "normal" dry fly is held off the water by the hackle and that it holds a bit of the tippet off/above the water also, so that the tippet hangs at an angle before becoming submerged and if that is so the up-eye would suspend more tippet higher above the water than a straight eye and the straight eye would suspend more tippet than a down eye. Of course if the fly is constructed to ride in the 'film" rather than on it this would be less apparent. I think the nearer to the hook the tippet enters the water the less noticeable the entry point would be.
I don't know that the fish even notice these things when keyed in on a fly until they have been caught many times but I do think they become conditioned or "trained" in areas of C&R.
In fish that are not often exposed to leaders and flies, it should not matter- if the theory of conditioning is the reason for refusals.