Confession time - I intervened manually to space systems in a few parts as needed, instead of specifying universal defaults in Layout Options. Lesson learned. 
Meanwhile, is there a way of clearing manual adjustments to this vertical spacing to clear the naughty manual intervention?
Gosh, there’s a lot to cover in the manual.
Thanks again Lillie.
The manual is sort of stupidly broad, in some ways, but that should mean searching for most things will bring up helpful results.
(I did enjoy it being described as “almost frighteningly comprehensive” in this MyMac.com review of Dorico 4.)
There is nothing stupid about being all-encompassing. 
