I’ve sort of settled on the high uchiokoshi and daisan, then lowering the left shoulder gradually during hikiwake, though it will be a while before that happens smoothly. At the same time I figured out why the bow and the left arm were dropping at hanare. When the left shoulder was up I must have been pitching the left hand slightly down to compensate. Today I tried tilting it ever so slightly up at kai, and this helped, not reducing the drop at hanare, but also a more vertical yugaeri, instead of the bow itself pitching forward.
So many things in flux, and they’re all connected.
Practical note for the future: Yamato Takkyubin won’t transport bows because they’re too long to fit in their smaller trucks, but you can use Yamato-bin. Costs about ¥2,500 from Hokkaido to Tokyo, including insurance.