How to lengthen stems in beamed groups

[Knute Snortum]

Hi list,

I'm hoping someone can give me insight into how to lengthen stems in beamed
groups globally.

LilyPond usually makes good assumptions and has great defaults, but in this
situation it fails to create good stem lengths in beamed groups.  I've
attached some sample code that illustrates the problem.  With the following
line commented out, you can see that the stems are too short
(stem-too-short.png):

\override Stem.details.beamed-lengths = #'(3.5 4.1)

With the above line uncommented, the stem lengths are better, except the
second measure, right hand, third beat (stem-lengths-better.png).

My questions are these: How do I tell LilyPond what length the shortest
stem in a beamed group should be? (I tried playing
with Stem.details.beamed-minimum-free-lengths, but its behavior seemed
chaotic.)  And is there a better way to control stem lengths in beamed
groups?

--
Knute Snortum

\version "2.24.3"
\language "english"

global = {
  \time 12/8
  \key f \major
}

rightHand = \relative {
  \global 
  d''4.~\startTrillSpan d16\stopTrillSpan c bf a g f  bf8 g' e!  c bf g' | 
  \noBreak 
  a,16 g f e f a  d, f d bf g e'  f bf, a g a c  f,4 r8 |
}

leftHand = \relative {
  \global
  \clef bass
  f16 d bf a bf d  f, bf d f e! d  e c bf a bf c  g bf e g f e |
  f8 a, d  bf8.\trill a32 bf c8  f,4 r8  r16 c' a c f,8 |
}

\score {
  \new PianoStaff <<
    \new Staff \rightHand
    \new Staff \leftHand
  >>
  \layout {
    indent = 0
    \context {
      \Score
      % defaults = #'(3.26 3.5 3.6)
      \override Stem.details.beamed-lengths = #'(3.5 4.1)
      % defaults = #'(1.83 1.5 1.25)
      %\override Stem.details.beamed-minimum-free-lengths = #'(1.83 3.33)
      % defaults = #'(1.0 0.5 0.25)
      %\override Stem.details.stem-shorten = #'(1.0 0.5 0.25)
    }
  }
}