staff collision because of a postscript line

[Stefan Thomas]

Dear Lilypond-users,
in the below quoted snippet I get a collision between the two staves.
Is there a possibilitie to avoid automatically this collision, without
increasing the distace between the two staves generally?
Here is the snippet:

\version "2.12.0"
%%some definitions
  onBeat = \markup { \postscript #"
    0.1     setlinewidth
    0.5 4   moveto
    0.5 0   lineto
    0.2 0.6 lineto
    0.5 0   moveto
    0.8 0.6 lineto
    0.5 4   moveto
    3.5 4 lineto
    stroke
    "}
    standardped = { \override Staff.PianoPedalBracket #'style =
#'bracket \set Staff.pedalSustainStyle = #'mixed }
    smaller = {\set fontSize = #-3 \override DynamicText #'font-size =
#+3 \override TextSpanner
      #'font-size = #+3 } %noten so schnell wie moeglich; Dynamik und
TextSpanner normale Groesse
      % das habe ich bisher noch nicht benutzt
      normal = {\unset fontSize \revert DynamicText #'font-size
\revert TextSpanner #'font-size } % Noten und Dynamik normale Groesse!

      %%%%%             the music itself
%%%%%%%%%%%%%%%%%%%%%%

      UpStaff = \new Staff \relative c {
        \clef bass  \scaleDurations #'(32 . 35) { \standardped
        \smaller f32[\f\>^\onBeat \sustainOn g e] \normal dis1
\sustainOff \p } }

      DownStaff = \new  Staff \relative c { \clef bass
\scaleDurations #'(32 . 36) { \standardped
        \smaller a32 [ \sustainOn \f \>^\onBeat c cis d ]  \normal es1
\sustainOff } }


      \score { << \UpStaff
        \DownStaff >> }