LSR : Dashed slurs indicating optional slurs between lyric lines

[Pierre Perol-Schneider]

Hi Squad,

In this snippet : http://lsr.di.unimi.it/LSR/Item?id=308
the slur is to low.
So I'd like to slightly change it to :

\version "2.18.2"

\score {
  <<
    \new Voice = "melody" \relative c' {
      c8 e8
      <<
        {
          d8 f8
        }
        \new Voice {
          \omit Stem
          \override NoteColumn.ignore-collision = ##t
          \slurDashed
          d4*1/2 -\tweak line-thickness #2.5 ( f)
        }
      >>
      \oneVoice
      e8 g8 f8 a8
    }
    \new Lyrics \lyricsto "melody" {
      One two three four five six seven eight
    }
    \new Lyrics \lyricsto "melody" {
      One two Whee! \skip 4 that's a dashed slur!
    }
  >>
}

Any objection ?

Cheers,
Pierre