Dear All,
Regarding vertical stretching of staves, have you looked at Trevor Bača's "Controlling vertical spacing exactly - mini HOWTO"
in which he says:
1. First, it seems that there are two *different* models for
controlling vertical spacing, which we might term "permissive" and
"strict", respectively.
Your description of vertical spacing is quite good (although I think it might be possible to make staves overlap in the "permissive" mode: try setting VerticalAlignment ´padding to something negative). However, the distinction between PianoStaff and other staff groups has disappeared in 2.11; forced-distance no longer works.
Joe