I’m unable to reduce the text size from 13Px in the mobile editor for site editor.
Hey, I just had the same then I realised this only applies to the ‘mobile’ text that you add via the mobile site. If you have text in your desktop version that’s carried through into your mobile site then you can adjust that via the - and + icons that appear when you click on it. I think any new text that you add on mobile will be 13px plus. Hope this helps.