staff spacing

[Russ Ross]

Hi,

I'm setting the full score for the first movement of Bach's St.
Matthew Passion which has about 27 staves per page.  I can squeeze
them all onto a single A4 page by scaling down to the 11 pt size,
moving a few dynamic marks, and increasing the textsize parameter.

When the vocal parts are resting, the system crunches down to a much
smaller size (no lyrics) which I'd like to avoid.  What I'd really
like is to fix the spacing of the staves on all pages to be the same,
ideally computed based on the largest spacing needed on any page.
Is it possible to do something like this?  I think it makes the
music much easier to follow from page to page.

I've tried setting the spacing of an individual manually using:

  \property Staff.minimumVerticalExtent = #'(-3 . 5)

or something similar, but this seems to expand the staff too much on
the pages with lyrics (where space is tight) and not enough on the
pages without lyrics.  Is there another setting that controls the
inter-staff spacing when lyrics are involved?  If I can just set the
spacing myself it should work with some trial and error.  If I could
get lilypond to compute the spacing and keep it the same for all
pages that would be even better.

Any suggestions?

Thanks,

Russ