I have found a very useful short but sweet piece of guidance on a website this evening that has helped me understand some of the engraving setups within Sibelius that I can try to apply to my score.
The ideal distance between staves varies; this is based upon the number of staves, the page size and system size, and the number of systems on a page.
If one considers the braced Grand Staff, the ledger line on middle C is a staff line. The braced grand staff functions as a bridge between two different clefs, in turn moving the treble and bass clefs closer together and making middle C directly entered between the two. So there are two staff spaces between the clefs, the one staff space above, and the one staff space below middle C.
Sibelius measures this distance from outside the staff lines and calls it ‘2 spaces’.
You can change the vertical distance globally (yes – the entire score in one go!) for all staves by changing the vertical space. In Sibelius, you do this in Appearance>Engraving Rules>Staves>Layout.
If one considers the space between staves and how it corresponds to the distance between staff lines, this is a good way to visualise and appropriate distances. For orchestral scores, a good starting point for vertical staff spacing might be 8 ledger lines deep (Sibelius calls in 8 spaces, measured between the bottom and top staff lines of 2 adjacent staves).
You can also change the vertical space between groups of instruments in the same Engraving Rules as above, and you can increase the spacing even more if needs be in Extra Space vs Groups. For extra room above the strings group for tempo/rehearsal marks, change ‘Extra space above for system object positions’.
Staves will auto-justify automatically unless the value in Engraving Rules is set to 100%. I was a victim of this when I initially tried manually manipulating my stave positions and they kept snapping away from me!
Puff, R. (2013). Vertical Spacing Between Staves In A Score & Working at 100%. Available: http://www.rpmseattle.com/of_note/vertical-spacing-between-staves-in-a-score-working-100/. Last accessed 05/12/2016