When I started learning jazz on the piano, I was shown a very good exercice to learn voicings in all scales. It started Am7-D7-G7M-C7M-F#dim-B7-Em7-Bb, then it went on the same from Bbm7-Eb7-... It was pretty hard to get it all right, but in the end it got to teach you good voicings for every single 2-5-1.
Is there something similar for the chromatic accordion? (ideally with fingering for B-system)