Peter,
In previous posts in the alto forum I have made a more general assessment of Yepes tuning. To repeat, while most 10s guitars show some improvement, with some it is dramatic, with others it is barely detectable. Consequently, construction plays a part. I am working on a theoretical model that may help explain why this is so. However, it has to compete for my time with that spent on my musical interests.
I do not use Yepes tuning for the simple reason that it is inappropriate for the repertoire I play. I do not play anything resembling standard repertoire. I have only one 10s in E, a respectable Chinese instrument, other ms instruments range from D to A. However, when talking to any guitarist considering taking up a 10s instrument, I always encourage them to try Yepes tuning, along with romantic tuning. I find most just want extra bass strings, even though this may add to the imbalance of the instrument.
I agree that the trebles in a standard 6s instrument are not uniform, but the lack of uniformity is not so obvious as to render the instrument seriously defective, certainly as judged by an audience.
My Ramirez in E arrived in Yepes tuning. After about three days experience, I concluded that it was essentially a 7s instrument with some optional extras. I therefore viewed it as suitable for standard repertoire plus. I was not overwhelmed by the 'enhanced' response, and put it in romantic tuning. In this tuning it was bass heavy, but with a sweet treble. I subsequently loaned the instrument to Graham Divine to play the Ohana cycle in recital, having put it in Yepes tuning. When returned, having been played extensively for some months, it was a different instrument. I had previously wondered whether I should put it in D, as it was so bass heavy. On an impulse, and with some misgivings, I put it a tone up in F#, to simulate renaissance G tuning. (Strings from Hannabach.) The balance and projection were both better than those achieved with either romantic or Yepes tuning. So, the frequency response spectrum of the instrument plays a part. I have kept it in F# tuning ever since.
The total energy-kinetic plus potential- of an overtone depends inversely on the square of the number of the overtone, so, energy does fall off quite quickly. A small counterbalance to this is a term, (sin(npia/l))^2 in the numerator. Here, n is the number of the overtone, l is the vibrating length, a the distance from the nut or pressed fret to the point of plucking. As a increases, so does this term. To appreciate the overall effect, it is better to work out the total energy of the overtones in successive octaves, with different values of a. When this is done, one can see that as the overtones begin to cluster into successive notes in the higher octaves, increasing a, i.e., playing nearer the bridge, does increase the total energy going into the overtones at the expense of the fundamental.
James.