Keep System Text size independent of Performance Text size

When I change Performance Text size, System Text size changes with it.

I would like to be able to set System Text size independently of Performance Text size - or at least have System Text remain at a default size.

I use System Text for important (structural) stuff like 'To Coda', which needs to be large and visible.
I use Performance Text for all sorts of random stuff (per part), and sometimes it need to be tiny.

I have one score where I'm repeating measures instead of using DC al Coda, because I need some tiny Performance Text, and the 'DC al Coda' and 'To Coda' System Text would be too small to be useful.