\version "2.15.8"

col = \markup { \column { 6 5 } }

\score {
  { c'_\col }
  \layout {
    \context {
      \Staff
      \override TextScript #'baseline-skip = #2
    }
  }
}

\score {
  { c'_\col }
  \layout {
    #(layout-set-staff-size 24)
    \context {
      \Score
      \override StaffSymbol #'staff-space = #(/ 24 20)
    }
    \context {
      \Staff
      \override TextScript #'baseline-skip = #2
      %% The following scales correctly
      %\override TextScript #'baseline-skip = #(* 2 (/ 24 20))
    }
  }
}