I really appreciate your insights, Hans, as well as those of others who have studied ballet seriously and even taught.
I hope I didn't frighten people away from replying--as with everything in ballet, one needn't know every tiny rule about Úpaulement to have an opinion about how it looks and/or who does it well.
Although I understand the reasoning behind the split between BT and BT for Dancers, I often find myself wishing that those of you who truly understand the technique beneath and within the dancing would talk MORE about what it is that you see and experience during performance.
The concept of "opposition," as presented in drb's post, seems crucial. In Renaissance and Mannerist sculpture, the opposition (often referered to as "torsion") tends to between upper body and lower body -- a kind of twisting of the spine.
The influence of Hellenistic sculptures like The Dying Gaul and Laocoon on artists like Michelangelo and Caravaggio is unquestioned. Comparison of representations of the human figure with this tension and without it -- for instance, Michelangelo's Pieta versus Piero da Cortona's -- is striking. The artists who use this more elaborate version of epaulement produce figures that "live" in the way that other, more conventional artists, could not.
It may be an optical illusion, and I don't understand it, but the effect is definitely there. So why not in ballet as well?