tie collisions

[Olivier Vermersch]

Hello,

This is an example of collision between a tie in the middle voice and a
note in the higher voice (I use lilypond 1.4.9):

\include "paper20.ly"

melone = \notes \relative c'' {
  b8 a gis4 fis8 cis' fis4 ~ |
  fis8 b, gis'4 ~ gis8 cis, a'4 ~ |
  a8 dis, b' a gis gis16 a b8 a16 gis |
}

meltwo = \notes \relative c' {
  eis8 fis4 eis8 fis4. a8
  d4 ~ d8 b e4 ~ e8 cis
  fis2 ~ fis8 b,16 cis d8 cis16 b
}

melthree = \notes \relative c' {
  gis cis, a' cis, b' cis, cis' b a b cis b a gis fis e!
  b' cis d cis b a gis fis cis' d e d cis b a gis
  dis' e fis e dis cis b a e'2 ~
}


\score {
\context PianoStaff
\notes
<
  \context Staff = "up"   <
    \time 4/4 \key a \major \clef G
    \context Voice = VA { \voiceOne \melone }
    \context Voice = VB { \voiceTwo \meltwo }>

  \context Staff = "down" <
    \time 4/4 \key a \major \clef F \melthree>
>
}


I've tried to tune the ties by precising control points, but with this
hack the tie is incorrect when you change the paper size. Is there a
proper way to handle this ? What can I do ?

Thank you,
Olivier Vermersch