ChordNames context with bar lines - vertical spacing issue

[Piotr]

Hello, I am trying to design a simple chord sheet in LilyPond - just chords
and bar lines. I found this snippet at the repository, that enables me to do
that without creating any staves: (http://lsr.dsi.unimi.it/LSR/Item?id=460)

\new ChordNames \with {
  \override BarLine #'bar-extent = #'(-2 . 2)
  \consists "Bar_engraver"
}
\chordmode {
  f1:maj7 f:7 bes:7 f:7 \break
  f1:maj7 f:7 bes:7 f:7
}

My problem is that the vertical spacing between the lines leaves quite a bit
of empty space. How can I decrease the spacing? With staves it is simple,
but there is no staves object here...

Thank you!
Piotr