too much space for text

[Stefan Thomas]

Dear lilypond-users,
in the below quoted example the text takes, in my opinion, too much space, athough I wrote the command \textLengthOff.
How can I avoid it?
Here is the snippet:

\version "3.11.60"
ganzunten = {\clef bass
        \textLengthOff 
        \ottava #-1 
        %es wird zweistimmig!
        << 
          { \oneVoice <a,,, \harmonic b, \harmonic > 1 ~ ^\markup { \teeny \italic "(Cluster stumm niederdrücken, mit drittem Pedal halten" }
            
            \repeat unfold 2 {  <a,,, \harmonic b, \harmonic > 1 ~ }
          <a,,, \harmonic b, \harmonic > 4~  <a,,, \harmonic b, \harmonic > 8  r8 r2  } \\
          { %die zweite Stimme
            {    \makeClusters { <c,,  g,  > 32 <c,,  g,  > 32  } s16*15 |  }
        
              }
        >>
   
        \ottava #0  }
\new Staff { \ganzunten }