How to control beamed stem length to avoid collision?

[steve]

  Howdy!

              For some reason lilypond ( 2.18.0) doesn't get this correct
straight
out of the box, though there is lots of room for slightly shorter stems...
shouldn't
need to move the note column...

http://www.gooeytar.com/projects/test/granada_test.pdf

          How do I fix this stem collision?

       Using this thing will lengthen stems but not shorten them

\once \override Stem.details.beamed-lengths = #'(7)
\once \override Stem.details.beamed-lengths = #'(2)

       Code below..

          thanx - steve

*****************

\version "2.18.0"

\paper { }

\header { }

#(set-global-staff-size 19)

 first = \relative c' {
    \set Staff.instrumentName = "Guitar "
    \set Staff.connectArpeggios = ##t
    \key e \major
    \tempo "Allegretto"
    \tuplet 3/2 { e16([ fis e) } d8]~ d8~ |
 }

 second = \relative c' {
\once \override Stem.details.beamed-lengths = #'(1)
    < g b >8 < g b > < g b > |
 }

 third = { }

 fourth = \relative c {
    g4.
 }

 guitar = << \first \\ \second \\ \third \\ \fourth >>

global = {
    \clef "G_8"
    \time 3/8
    \set harmonicDots = ##t
    \set Staff.connectArpeggios = ##t
}

\score {
  \new StaffGroup \with {
            \consists "Span_arpeggio_engraver"
            \override StaffGrouper #'staff-staff-spacing =
                #'((basic-distance . 12)
                   (minimum-distance . 8)
                   (padding . 2))
            }

             <<  \global \guitar >>

 \layout { }
}