How to increase the length of an arpeggio

[Nick Payne]

How can I increase the length of the arpeggio bracket on seconds and 
thirds, which at their default lengths are ridiculously short. See 
attached example. I'd like to make the length of the arpeggio on seconds 
and thirds the same length as that on the fourth. I tried various 
overrides such as \override Staff.Arpeggio #'Y-extent (which had no 
effect at all with any values that I tried) and \override Staff.Arpeggio 
#'position (which caused the arpeggio to disappear with all values that 
I tried, along with warning messages saying "no head found for arpeggio".

I guess I can get what I want by creating an additional hidden voice 
with arpeggiated notes at the right pitch to lengthen the arpeggio, but 
was wondering if it is possible to get what I want with an override.

There's also the problem with arpeggios that they don't get spaced 
properly from the preceding note. Usually it just means that they're a 
bit close, but if the preceding chord contains a second then they 
actually overlap the note.

%======================================
\version "2.13.4"

treble = \relative c {
   e\arpeggio f\arpeggio g\arpeggio
}

bass = \relative c {
   d\arpeggio d\arpeggio d\arpeggio
}

\score {
   <<
       \context Staff = guitar {
           \set Staff.connectArpeggios = ##t
           \clef "treble_8"
           \key c \major
           \time 4/4
           <<
               \context Voice = "1" { \voiceOne \treble }
               \context Voice = "4" { \voiceFour \bass }
           >>
       }
   >>
   \layout {
       \context {
           \Staff
               \consists "Span_arpeggio_engraver"
       }
   }
}
%======================================

Nick