I’m writing a continuo part; I’d like the bass line to be full-size and the right hand to be smaller, say 75%. This is a fairly standard design choice. If I set the keyboard part to, for example, harpsichord, then the size setting for the two staves is linked; I can’t have one one size and one the other. Bug, feature, or user error? I have figured out a work-around–leave the rh of the harpsichord empty and make a part with the full-sized bass part and the right hand of the harpsichord–but I wonder if there’s something better.
At the moment, as you’ve found, you can only change the size of all staves belonging to all players held by an instrument. We’ll think about whether we could relax that in future, though I believe what the program does at the moment is more useful as a default behaviour (for use cases such as cue staves, etc.).