Staff labels distance per part?

I wonder why the staff labels’ distance settings are located in the “Engraving”-section instead of the “Layout”-section. Thus the adjustments are applied on all layouts, and I cannot find a way to define them individually per layout.
With my settings the distances in the score are just fine (first example), whereas gaps are produced in the parts. Any solution?

No, there’s no solution for this. In general this doesn’t cause issues (particularly because it’s uncommon to use staff labels in parts, except in percussion parts), so it’s not something that has been requested before. I suggest you review your settings, as it should be possible to find a compromise that achieves acceptable results in both the full score and the percussion score.

I use staff labels in parts only in case of divisi changes. And I hid “1. Vl.” in the meantime.

I cannot further reduce the “distance between inner or only staff label…” since the numbers in divisi-labels would collide with the brackets. Of course I could enter a space after the numbers there manually…

Pragmatically … Consider omitting player numbers (group names) from the part entirely, because percussion sections often read off score and handle division of parts themselves. Even if you’ve fixed exactly who plays what, they will arrange the instruments following the listing on the first pages and not randomly switch instruments.

This is exactly what I intended - but I then noticed that Dorico “forced” me to think in terms of players (some instruments assigned to both of them). Therefore I had to revise the whole parts.
Of course I could hide the numbers, but then it would be unclear if only one staff/player appears in the part.
Is there a way to show the players’ brackets without numbers? This would be the best solution for me.
Or is there a better way to dispose the percussion parts? It was quite a hassle to figure this out, and I still don’t feel absolutely comfortable.

You can certainly change the bracketing at the beginning of each flow in engrave mode.

But if you have only one of each instrument, I would say don’t even worry about the bracketing.