Resize \rhythm in mixed markup

[Thomas Morley]

Hi,

consider below

\version "2.24.0"

\score {
  { g'1^\markup { My Rhythm \rhythm { 8[ 8] } } }
  \layout {
    \context {
      \StandaloneRhythmStaff
      fontSize = #6
    }
  }
}

I'll have numerous such markups combining straight text and \rhythm.
Thus I'd like to have a method to adjust the \rhythm-part in a
score-layout without affecting other parts of TextScripts.
Alas the setting fontSize takes no effect.

How to?

Cheers,
  Harm