Working with a space size of 1.15mm, if what you want is 8mm between staves, 10mm between players and 14mm between systems, those values in Layout Options should be something in the region of 7 spaces, 8 5/8 spaces and 12 1/8 spaces. That said, you should go lower as Dorico pays attention to items that protrude from the staves and these are really minimum values - it will tend to push music onto the next page in order, erring on the side of roominess.
You can counteract that to a degree by turning off Automatically Avoid collision between staves and systems (in the same bit of Layout Options), or by reducing the minimum gaps there.
You also have the vertical justification settings at their default values in all of the layouts, meaning that it a page is more than 60% full it justifies all of the gaps between staves and systems. As in your first screenshot this is a poor choice for a combination of staff size, page size and number of staves that results in there only being two (four-staff) systems on a page. I’d be tempted to set the next option down from 80% to 60% so that it consistently spreads the extra space between systems rather than between staves.
One thing you could do to give yourself more room - you’ve done this manually on page 2 - is to reduce the bottom music frame margin (again in Layout Options, I believe in page setup - sorry, I’m not currently in front of Dorico).
The manual spacing adjustments you previously made were relative to the vertical spacing settings that were in place at the time, e.g. Dorico tells you that the lower staff is 8mm from the top staff, but that’s calculated entirely as whatever the default distance is +/- the adjustment that you made. If you change the vertical spacing settings now, your manual adjustments will remain intact, but relative to the new settings. As I said earlier, to Engrave > Staff Spacing > Reset Layout (and maybe perform all this on a copy of the original file, so that in the unlikely event that you can’t persuade Dorico to do what you want automatically, you still have your previously manually adjusted version.)
I guess the bottom lines are:
- Don’t work a two piano piece in a part layout with the default (or nearly default) part layout settings, as in your first screenshot.
- Try to find a happy medium with Layout Options before you start manually adjusting staff spacing.
- Don’t use Make Into Frame or Frame Breaks set to Wait for Next while you’re still inputting music (and this includes pedal marks and accidentals).
Things are going to change as the music is entered and adjusted, so really try to resist touching anything in Engrave mode (at least in the Note Spacing, Staff Spacing and Frames sub modes) until you’re truly done with Write mode .