Am I correct in thinking that I can’t change the size of a 6/9 component other than editing the chord itself? It doesn’t seem to be affected by either sub/superscript scale factor or stacked alteration scale factor. 6add9 works fine but any of the other 4 options are unaffected.
You’re right, those glyphs don’t change for me either. Being honest, Dorico doesn’t have enough options with 6/9 chords. I don’t typically use a / here as it’s not a fraction and I don’t use a / with any other stacked alterations, but Dorico doesn’t provide that option. Major and minor 6/9 chords are the two chord qualities that I just ended up creating my own for every variant back when I first started using the program.
You can make a global change to the composite glyph though. In Project Default Chord Appearances, enter a 6/9 chord, hit + so it now is showing in the window. Click the 6/9 so it should show as selected in the panel underneath with multiple glyphs. Click the Edit Component pencil, and now you can make a global change to that composite glyph in the Edit Chord Symbol Component window which should allow you to resize it as needed.