Every time you post Jack, I/we learn something else. Thank you. I was unfamiliar with the term 'Arch contour' and have familiarised myself via Wikipedia.
Interestingly the last time I heard Overtone singing (Bebey's last note) was in a recording of an African (can't remember where) woman, that was played at a lecture at Loughborough Uni. I was also thinking in terms of a pentatonic scale at the beginning of this thread. I can hear major pentatonic now you have it suggested.