4
Oddly enough, I deleted all my test stories and wrote a new one and that one displayed in the "Big Story" box first thing... Perhaps I added the "Big Story" feature after the original stories had been written!? I dunno, but it's working now...
UPDATE: Now that it's working, it's clear that it's simply hits that make the difference (I can watch it change as I raise and lower the hit total by clicking on each one).