For full disclosure I've never flown the 737, and I only learned about the existence of the STS probably the day before I made the post. I only slotted the info from the quoted manual section, as well as Mad (Flt) Scientist's blurb from the Lion Air thread, into the basic framework of how trim and speed stability works in flight dynamics. So if there are any subtleties to the system, beyond what's written here, that might change how it works in a non-obvious way, I wouldn't know about them.