\crossStaff confusion

[Mark Probert]

Hi, again.

I'm not used to working with piano scores and ran across and example 
that required I use \crossStaff. Unfortunately, it is not doing as I 
ask it and wonder if someone can point me in the right direction.

In this example I want an arpeggio line and I want the C in the bass to 
be joined (and at the correct value to) the voice above it. 

As an aside, the convoluted structure helps me in doing this art song 
setting as there is a voice line above the piano (not shown) and I 
wanted this example in context.

TIA .. mark.

---- code

\version "2.22"

\layout {
  \context {
    \PianoStaff
    \consists #Span_stem_engraver
  }
}

upA = \new Voice \relative c' {
  \voiceOne
}

upB = \new Voice \relative c' {
  \voiceTwo
  <b d'>8\arpeggio r8 r4 r2
}
dwA = \new Voice \relative c {
  \voiceThree

}
dwB = \new Voice \relative c {
  \voiceFour
  \crossStaff { c8 } r8 r4 r2
}

{
  \new PianoStaff <<
    \new Staff {
      \upA
      \upB
    }
    \new Staff {
      \clef bass
      \dwA
      \dwB
    }
  >>
}