That's some of the mystery involved with euro-nymphing. I had tried to use this approach (poor success with "euro leaders") nonetheless successful on fish take. I do agree with your evaluation of needing to make some changes--but simply put how many times do you have to adapt the length of your leader to fit certain situations. I know that if I am locked into euro style on a particular day and I have tried for 45-60 minutes without success I certainly would be changing tippets for a longer length and a heavier dropper. My eye is on the "sighter" and I do my mending as dictated by the stream speed. "Leading" the fly is a condition I haven't really thought of I guess what I do after all these years is "instinctive?" "Doc"