Hi David, you are looking for markup-system-spacing:
\paper {
markup-system-spacing.basic-distance = #10
}
Flexible vertical spacing \paper variables:
http://lilypond.org/doc/v2.20/Documentation/notation/flexible-vertical-spacing-paper-variables
Cheat Sheet:
https://joramberger.de/files/LilypondSpacing.pdf
Best,
Joram
