Stretching of nested GrandStaff inside StaffGroup?

[Reinhold Kainhofer]

I'm currently fiddling with the vertical stretching of large orchestra scores, 
where the string section is a StaffGroup with a GrandStaff for the violins and 
a 
normal staff for the violas. The problem is that the viola staff is stretched 
avail from the GrandStaff by the same amount as the top-level StaffGroups are 
stretched. I can't seem to find the proper spacing settings to keep the viola 
staff together with the violin grand staff (i.e. stretched just like the two 
staves in the first staff group for the brass).

Attached is a sample file showing the problem.

How can I keep the viola staff closer to the violins?

Thanks,
Reinhold
-- 
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Reinhold Kainhofer, address@hidden, http://reinhold.kainhofer.com/
 * Financial & Actuarial Math., Vienna Univ. of Technology, Austria
 * http://www.fam.tuwien.ac.at/, DVR: 0005886
 * LilyPond, Music typesetting, http://www.lilypond.org

spacing-understanding.ly
Description: Text Data

spacing-understanding.pdf
Description: Adobe PDF document