Why do chords print below staff?

[Peter F Whyte]

I used to get chordnames printing above the staff, but now they always, 
always print below.  Nothing I try to change seems to have any effect on 
the position whatsover. I've searched the entire archive, but all to no 
avail.  Hoping desperately someone can help.  This is the third time I've 
tried to solve the problem, and it's taken 3 hours of absolute frustration.

I'm using Win XP Pro SP2 with lilypond 2.4.2 (can't bear to change the 
version again as it took ages last time to get things sorted, and it works 
ok, except for this problem).

I've parts all in a separate file and an include line which works fine.  
Here's my score section.  I'm looking for chords on top, melody line 
next, lyrics below this, and piano staff at the bottom. It all works fine until 
I add the chords - they always go to the bottom, never the top.


\score {

  <<
      \context ChordNames {
                \set chordChanges = ##t
        \guitar
      }
        \context Voice = mel { 
                \set Staff.instrument = #"Melody"
                \set Staff.instr = #"Mel"
                \global \Key \melody  
        }
        \lyricsto "mel" \new Lyrics \text 


        \context PianoStaff = "piano" \piano
        
  >>
        
% ------ common to all scores ------
  \layout { 
    \context { \RemoveEmptyStaffContext }
    linewidth = 180.0\mm
        \context {
          \Voice
          \consists Ambitus_engraver
        }
  }
  \midi { \tempo 4=110 }  
}


--
Peter F Whyte
Belfast (N Ireland)