Practice yesterday was a mixed bag. I tried a couple of changes to my tenouchi in combination with the new daisan position, but nothing seemed to have much (positive) effect. My teacher noticed and essentially corrected me back to the way I was on Thursday: new daisan but nothing else changed. Perhaps he wants me to get used to that first, then refine it. The effect remains clear though… much better accuracy.
The difference I’m talking about is seen in this diagram from Minna no Kyudo (pg. 90),
though to make it more effective you have to see it from the archer’s point of view from daisan into kai. My problem was the position highlighted in yellow, and all it took was turning the wrist (and forearm bones) to get the straight line in the photo. I suspect that shamen archers don’t have this problem because they set their left hand before uchiokoshi and don’t have this intermediate stage where the bow needs to turn in the hand.
My problem now is (or seems to be) getting the form of tenouchi and the amount of force applied in various places back into the right balance. The reason I was getting into the hairisugi position in the first place was to get the bow turned around so that its inner edge would line up against the tenmon line, so I suspect the root of all this is a tenouchi problem that has been there all along. Step by step, I guess.