Rule for space between changing instrument and condensing

How does Dorico calculate how much space is required before an instrument change allows for condensing?

For example, 2nd flute is playing piccolo, then switches to flute, and has music to play 6 measures further.

For some reason, despite the last piccolo note being on one page and the first flute note being on the next page, Dorico isn’t letting me condense the 2 flute parts onto one staff. It’s giving me one page of two separate staves, and then on the 3rd page it’s finally condensing the two flute parts onto a single staff.

The images show the result:



It’s not about how much space is required—this would still happen with 60 or 600 empty bars before the Flute 2 entrance. The issue is that despite the graphical options you’re given in Layout Options > Players > Instrument Changes, ‘under the hood’ there’s still some kind of switch happening [exactly on the second beat of bar 50]*. Whichever staff that specific point falls on can’t be condensed. I do not pretend to know why this is still the case. The only true workaround I can give you is to have your Piccolo in a separate player, put in all instrument changes manually as staff text, and babysit the staff visibility.

*/ EDIT: in experimenting just now I’ve found that the critical switching point is, in fact, on the preceding barline. Provided there’s a system break on that barline, you can manually condense the Fl 1 and (empty) Fl 2 before that point together into one.

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EDIT 2: Scratch that—if you manually condense a non-empty Flute 1 staff with an empty staff in Flute 2/Piccolo limbo, what you get is a staff full of rests.

In conclusion, the only true workaround is the one I already gave you, which can add a lot of work to a sizable score.