Based on the available space at the bottom of p2, the height of that last system, plus the inter-system gap, Dorico’s calculated that there isn’t. Sometimes Dorico gets that wrong thanks to a circular problem when it comes to casting off - as explained by Daniel e.g. here -
You can force the last system onto the 2nd page by adding a frame break at the top of page 2 and setting that break to “Wait for next frame break” in the Properties panel, or you can fiddle with your vertical spacing settings a bit.
Reducing the gap between staves to 5 and the gap between systems to 8 pulls it onto p2, but that puts p1 under the minimum threshold for vertical justification. If you increase the 2 values for vertical justification to 60 and 95 respectively, both pages will be vertically justified, but p1 will have both staves and system justified (filling out the page a bit more). It you’d rather keep the staves close together, and have any extra height left on the page only put between the systems, reduce the 2nd vertical justification value to 60/70%.
You might also want to reduce the minimum gaps a fraction - this is extra space added between staves/systems when other protruding items are present, like lyrics and dynamics.
Same problem, same question that happens often in other cases with this example, I hope more explicit than the later: Quand nous partimes de France Beta.dorico (382.2 KB)
Why can I not add more space between the staves of the first page ? I can do it manually, in Engrave menu > Staff spacing, but in Layout option > Vertical spacing > Space between systems, I cannot go higher than 9 spaces otherwise the fourth staff jumps to the second page.
It seems that Dorico dont like the staves go lower than this blue margin who appears in Engrave mode > Space between staves :
Set the vertical justification to e.g. 70% and watch the magic happen.
The bottom blue area is the music frame margin. You can change this (and indeed the page margins) if you like. The bottom music frame margin controls the gap between the page margin and the bottom staff line of the lowest staff on the page (assuming the page is vertically justified).
If the overall height that music takes up on the page is too much, you could increase the music frame margins to squish the music into the middle a bit more. There are various options in this area - including reducing the height of the music frame in which they’re shown.
@Koenraad, the vertical justification settings were indeed what you want, but you were caught in a trap that is one of Dorico’s current weaknesses: justification is for staves and notes, but it doesn’t currently take lyrics into account.
The way around this is to set the proper justification settings (in this case 70% is enough, and then also change the music frame bottom margin to something large enough to accommodate your lyrics. (Hopefully future versions of the software will take this into account automatically.) In this case 0.4" works for me.
When you do this at first, it thinks that the frame is too full, so the 4th stave pops onto the next page. To fix this you can use frame breaks, or, to keep it all automatic, lower the default distance between staves so Dorico doesn’t think the frame is too full. In this case, lowering the inter-system gap to 7 takes care of it. Alternatively, you can use casting off options to force 4 staves per page as well. This basically overrides some of vertical spacing settings.
It’s learning how these all work together that takes a bit getting used to, but once you do you’ll see how powerful they are.