tweaking voicefollower lines

[Shelagh]

How would you go about tweaking voice follower lines?
I want them to be unattached to the noteheads (eg shorter) and between the 
staves.
I tried something like this;


\override VoiceFollower #'extra-offset = #'( -1 . 0)

which made it look better, but is there a better property for determining 
the length of the
line? It looks like it ought to be the #'Y-extent-callback which requires 
a procedure and this is beyond me.


Shelagh