In case anyone's interested, in addition to...
- the under-thigh strap I'm now using to stabilize the concertina and to give me about 30% more air
- the swivel thumb strap I'm using to give hand flexibility in all directions
...I'm also now using a 'rail' mounted thumb strap (still swivels too) so I can slide to the higher range or back to get lower notes.
Video is at https://youtu.be/UIQoBGEBbjQ
Photo attached.
One thing I'd be glad to know is whether my junky old experiments Stagi tenor treble can have a bellows mod that will muffle it and give it a nice fruity tone like a Wheatstone.
Many months, someone gave me some good ideas about muffling, but I got distracted by a million things and have forgotten what they said.