Length 1: rise, fall
Length 2: rise-fall, fall-rise
Length 3: rise-fall-rise, fall-rise-fall (must be interchanging because for example fall-fall-rise would probably just be considered fall-rise)
In the Harry Potter example you can see that a higher frequency is very significant. But the exact frequency is probably rather arbitrary from book to book, whether there are ten peaks or five, say. So I'd imagine, over lots of texts, any particular higher frequencies is less significant, leaving the lowest modes to dominate, as you point out.
So overall, a rather uninspiring result, I felt.
Though if we're both missing something, it would be good to know!
Let me know if you are interested in investigating this properly.
non video description https://www.washingtonpost.com/news/wonk/wp/2015/02/09/kurt-...
the talk is funny though, i saw him give a much longer version.