Different staff sizes in different flows?

I think this may have been covered somewhere but I can’t find the reference.
How does one get different staff sizes for different flows?

Insert a system break at the very start of the second flow (i.e. in Engrave mode, select the first note of the flow, and type Ctrl+Alt+S): this won’t have any visible effect since there is already an automatic system break there, but it does then allow you to select the explicit system break and set a new global space size using the Properties panel.