Figured bass, horizontal alignment of pairs containing figures with accidentals

[Robert Blackstone]

Dear all,

As shown in the WME, in the figured bass line the figures with accidentals are 
"top-aligned", which I find rather unworthy of LilyPond.

See screenshot: 
https://www.dropbox.com/s/qff6p6t2i6j6ei7/Screenshot%202016-07-03%2009.51.40.png?dl=0

MWE:
%- - - - - - - - - - -
\version "2.18.2"

lower  = \relative c' {
      \clef bass
      \key f \major
      \time 4/4

         bes4 a g c  | %low-1
}

FiguredBass =  \figuremode {
< 5 3 >4 < 5 3- > < 5 3! > < 5 3+ >| %BC-1
}

\score {
        <<
        \new Staff = "lower" \lower
        \new FiguredBass \context "lower" \FiguredBass 


      \layout {
        \context { \Staff = "lower" \FiguredBass
     \override BassFigure #'font-size = #-2
 }
       }

%- - - - - - - - - - -

The ragged bottom line is undoubtedly caused by my making the figures a bit 
smaller, but the default size of the figures, and the size difference between 
figures and accidentals I also found very ugly and rather repelling. As far as 
the size of the figures and accidentals is concerned I'm happy with the present 
result.  

Is there a way to change the vertical position either of the accidentals or of 
the figures such that the figures with accidentals will be "bottom-aligned"? 

Thanks in advance for any help.

Best regards, 
Robert Blackstone