Vertical spacing isn't working...

[lilypond]

Probably because I've got the syntax wrong or something. Below is my wrapper 
.ly file with the details...

\version "2.4.0"

\include "english.ly"
\include "header.ly"
\include "voiceStaff.ly"
\include "voiceTrombone2.ly"

\header {
        title = "The King's Guard"
        instrument = "2nd Bb Trombone"
}

#(set-global-staff-size 14.14)

\score {
        \new Staff {
        \set Staff.minimumVerticalExtent = #'(-3 . 3)
                \set Score.skipBars = ##t
                 {
                        \clef "treble_8"
                        \transposition bf
                        \transpose bf c'
                        <<
                                \voiceTimeSig
                                \voiceTromboneII
                                \voiceMarkup
                        >>
                }
        }
        \layout {
        }
}

I want everything to fit on one page, and altering the font size has worked 
fine. It's just made everything too small for comfort ...

At one font size larger, I have one staff on page 2. Moving 
Staff.minimumVerticalExtent just triggers syntax errors. But whether it's there 
or not, or changing the settings (the manual says (-4 . 4) should bring your 
staves closer) doesn't seem to have any effect. What am I doing wrong?

Cheers,
Wol