Cracked it, you can now add more subtle overdrive, not just utter destructive filth: https://youtube.com/shorts/6xlVLJxJPlQ

I've got another week or two to spend tweaking the core distance : volume calculations, there's some notes playing with barely any attack/fade-in and it behaves differently on small phone screens versus tablets. The core behaviour and app is all finished now I think, just polishing left.