Stem length of beamed notes

[Francesco Napoleoni]

Hi everyone

While engraving the music in screenshot-source.png I’ve stumbled on a problem: 
I cannot adjust the stem height of the first couple of eighth notes to look 
like the printed version.

To be more specific: overriding the Stem.details.beamed-lengths does not work 
for me no matter which value I put between the parentheses. The relevant part 
is at line 6 of fragment.ly.

Any ideas?

Thanks in advance
Francesco Napoleoni

\version "2.23.5"

\parallelMusic voceUno,voceTre,voceQuattro,voceDue {
%% 18
  e2. |
  \override Stem.details.beamed-lengths = #'(2) g8 fis \revert Stem.details g a \once \stemUp b4 |
  e4 \stemNeutral s s |
  e,4. fis8 g4 |
}

musica = <<
  \clef treble
  \key d \major
  \time 3/4
  \set Timing.beamExceptions = #'()
  \set Timing.baseMoment = #(ly:make-moment 1/4)
  \set Timing.beatStructure = 2

  \new Voice {
    \voiceOne
    \relative c'' \voceUno
  }

  \new Voice {
    \voiceTwo
    \relative c' \voceDue
  }

  \new Voice {
    \voiceThree
    \relative c'' \voceTre
  }

  \new Voice {
    \voiceFour
    \relative c' \voceQuattro
  }
>>

\score {
  \new Staff \musica
}