I'd be interested in further
discussions on this topic

Me, too! My original post came as a result of a discussion I'm having
elsewhere. My assertion was that since most service manuals specify
10-4 as the right position, they are simply repeating "old lore" with
respect to hand propping. My interlocutor feels that whatever the
manual specifies is as a result of wanting to get the best performance
from the airplane. My response to this is that performance won't be
impacted, and that if anything, vibration would be the other issue, but
that this would be better addressed with a 12-6 positioning.