Vanessa
I had trouble posting a reply yesterday, sorry for the wait.
Those look like nagauta to me. It’s hard to tell perfectly, but the heights (especially the bone one) seem in line.
The black one could likely be used in min’yo however, it may be low enough.
Resonanace in a shamisen is pretty neat. It was explained to me by the shop owner at Sansui’en in Nagoya that there’s basically three sources of sound.
The initial strike
The circuit of vibration between the strings and koma, affected by the sawai
The resonance between the front and back skin and sides of the dou.
So everything matters!
Yes, on nagauta shamisens, the back resonator is key to getting a good sound.
I’ve never heard this before, but it wouldn’t surprise me. Nagauta skins are so delicate and thin that the addition support from your body could mess with it.
Pete, if you’ve got a hizagomu on your shamisen, you should be able to balance it on your leg with just your arm pretty safely - it bar you from bachitzuke, but it’s surprisingly stable.
One of my teachers had me practice just doing that for a while as I learned Mugiya bushi to practice form.