cross-staff beam from polyphon music

[Helge Kruse]

I have a new variant of cross-staff notes. When I omit the H in the 
upper staff and don't use polyphon music it looks quite nice, needs just 
some tweeks with dumping and so.

But there is one note that requires this <<{}\\{}>> construct, doesn't 
it? In this case Lilypond doesn't find a good slope for the second beam. 
How can this be solved? I already tried to write a similar <{}\\{}>> 
construct in the lower stuff. But it didn't help.

In the example below you find the left hand notes in the lower staff. 
Thats' the reason for the strange treble clef in the lower staff.

Regards
Helge


\version "2.16.0"
\language "deutsch"

upper = \relative c {
  \key g \major \time 3/8 \clef bass
  r8 fis e |
<< { h'4.-> } \\ {  %% skip this line, end it looks much better
    r32 d, fis h  d[ \change Staff=lower \clef treble fis h cis]  d 
\change Staff=upper \clef treble fis h cis
  } >>    %% you will have to skip this too
}

lower= \relative c {
  \key g \major \time 3/8
  R4. |
<h h,>4.\laissezVibrer |
}

harpPart = \new PianoStaff \with {
  instrumentName = "Harfe"
  \consists #Span_stem_engraver
} <<
  \new Staff = "upper" \upper
  \new Staff = "lower" { \clef bass \lower }
>>

\score {
<< \harpPart >>
  \layout {
    \context { \PianoStaff \consists #Span_stem_engraver }
    \context { \Staff \RemoveEmptyStaves }
  }
}