Vertical spacing between staves with lyrics and ones without

[Rodolfo Zitellini]

Dears list,
I have a little problem with the spacing between staves with lyrics.
When all the voices are singing and every voice has it's text,
everything is ok and evenly spaced. But when one or more voices are
silent the vertical space between the silent voices is reduced, giving
a very ugly layout, with the silent staves all compressed and a huge
space between the stave(s) with text.
Is there a way to tell lilypond to always space the staves with the
scape used when lyrics are present?
Thanks,
Rodolfo

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