Font-relative-size

[Rune Zedeler]

I didn't find any documentation of the aspects of the
font-relative-size...
Is it so that for music, setting relative-size 1 uses the "next" size...
I.e. that is for Paper20 relative-size 1 uses font size 23?
How about non notenames, i.e. scripts, chordnames, etc.?

If I want to calculate the fraction to use with i.e. #'staff-space from
the font-relative-size, is it then so that in paper23 frs1 corresponds
to 26/23 = 1.13 while in paper16 it corresponds to 20/16 = 1.25...?
I could probably make a Scheme Function doing this, but will I be
re-inventing the wheel? Have I misunderstood something?

-Rune