#(define ga_note-head-y-offset-callback
   (grob-transformer
    'Y-offset
    (lambda (grob orig)
      (let* ((cause (ly:grob-property grob 'cause))
             (pitch (ly:event-property cause 'pitch))

             (steps (ly:pitch-steps pitch))
             (middle-c-offset (- (* steps .5)))

             (semitones (ly:pitch-semitones pitch))
             (offset (* 1/3 semitones)))
        (+ orig middle-c-offset offset))
      )))


\new Staff \with {
    \override NoteHead.Y-offset = #ga_note-head-y-offset-callback
    \override Stem.note-collision-threshold = #1 % I want this to be 1.5
} \relative c' {
    <c g'>
    <c f>
    <c e>
    <c ees>
    <c dis>
    <c d>
    <b c>
}