\pointAndClickOff

incipitA =
#(define-music-function (parser location incipit-music) (ly:music?)
  #{
    \once \override Staff.InstrumentName #'stencil =
      #(lambda (grob)
        (let* ((instrument-name (ly:grob-property grob 'long-text)))
        (set! (ly:grob-property grob 'long-text)
          #{ \markup {
            \score
            {
              \new Staff
              {
                $incipit-music
              }
              \layout { $(ly:grob-layout grob)
                #(format #t "grob::cm: ~a " (module-ref (current-module) 'cm))
                scale-factor = #( / 1.0 (module-ref (current-module) 'mm) )
                #(format #t "test: ~a " (module-ref (current-module) 'scale-factor))
                #(format #t "indent: ~a " (module-ref (current-module) 'indent))
                #(format #t "short-indent: ~a " (module-ref (current-module) 'short-indent))
                #(format #t "incipit-width: ~a " (module-ref (current-module) 'incipit-width))
              }
              \layout {
                #(format #t "cm: ~a " (module-ref (current-module) 'cm))
                test = \cm
                #(format #t "test: ~a " (module-ref (current-module) 'test))
              }
            }
            }
          #})
          (system-start-text::print grob)))
  #}
)

\score {
  {
    \set Staff.instrumentName = #"Altus"
    \incipitA { f''1 }
  }
  \layout {
    indent = 10\cm
    short-indent = 1\cm
    incipit-width = 2\cm
  }
}