Chord accidental size in substituted fonts

[James Worlton]

Hello,

I'm writing a big band chart and having difficulty getting the main 
chords involving accidentals--B-flat, C-sharp, etc.--to look good with 
the lilyjazz font.

MWEs:
%OK size with defaults
\version "2.19.83"

\score {
  \new ChordNames {
    bes1
  }
}

%NOT OK size using lilyjazz
\version "2.19.83"
\paper {
  #(define fonts
     (set-global-fonts
      #:music "lilyjazz"
      #:factor (/ staff-height pt 20)
      ))
}
\score {
  \new ChordNames {
    bes1
  }
}

I can't find an override for the accidental size here after looking for 
the last couple of hours. Is there a way to reduce and/or move the flat 
in the second example?

Thanks,
James Worlton