To many clashing note

[Georges Roux]

hi,
have a warning:

clashing_note.ly:30:17: warning: ignoring too many clashing note columns

I don't understand why?

and is it possible to move the upper voice a little bit to the left to
prevent the collision?

Thanks
Georges

\version "2.5.32"
%\version "2.4.5"

\header {
  title = "Clashing note"
  subtitle = "to many"
  composer = "Jean Sebastien Bach (1685-1750)"
  style = "Classical"
  copyright = "Public Domain"  
  maintainer = "Georges Roux"
  lastupdated = "2005/07/10"
  filename  = "clashing_note.ly"
  instrument  = "Guitare"
  piece = ""
  }

global = {
    \clef "G_8"
    \time 3/4
    \key e \major
  }
  
midiStuff = {
  \set Staff.midiInstrument = "acoustic guitar (nylon)"
  }
  
upperVoice = \relative c' {
  \stemUp
  << { \stemDown b,16[ s e s fis s gis s a s fis s] } \\ { \stemUp s a16[ s a s 
a s a s a s a] }  >>         %110
  }

lowerVoice = \relative c, {
  \stemDown
  dis'4 \skip 4 \skip 4                                            %110
  }

Guitare = \simultaneous {
  \context Voice="upperVoice" \upperVoice
  \context Voice="lowerVoice" \lowerVoice
  }

\score {
  \context Staff="Musique" << 
    \midiStuff
    \global
    \Guitare 
    >>
  \midi { \tempo 4=108 }
  \layout {
    linewidth = 180.000 \mm
    textheight = 250.000 \mm
    }
  }
  
\paper {
    #(set-paper-size "a4")
    textheight = 24.0 \cm    % for A4 paper
    %textheight = 22.2 \cm    % for Letter paper
    }