I had this question closed, an action I accepted. However, just today someone posted this reasonably good answer to a similar question. I chased up the references and found some more details to add to my question, but as I was editing it I felt I was actually answering the question, although I do have some speculation in there.
Now, the original question was answered successfully for the scope given. The second one has a reasonable answer that might get accepted soon. My original question was classified as a dup of the original, although it might have more appropriately been marked as a dup of the second, but now my new version of the question tries to merge aspects of these two existing ones, but if we reopen my question will it now be marked a dup of the second? Or should my amendments to the question be extracted into an answer? If so, an answer to which question?