This is what has been said often URAKAMI SAKAE HANSHI.
「You should not twist your right hand when you are doing "YUGAMAE".
You twist your right hand gradually in accordance with the progress of "UCHIOKOSHI".
When "UCHIOKOSHI" is over, you slant the back of your right hand slightly so that the back of your right hand won't face upward.
Brirg it to your right shoulder keeping the hand as it is, then you can get the twist to work well.
You should not twist any more in the "KAI".
Keep stretching out your arm and shoot.」
The following is the original text of the Japanese.
「勝手は弓構えでは、まだ捻ってはいけない。
勝手は打起しと共に徐々に捻っていくが、打起しが終わった時に勝手の甲が天井を向いていたら、それはもう捻りすぎだ。
打起しが終わった時には勝手の甲が少し斜め上を向くようにし、それをそのまま肩まで持って来るように。
勝手の捻りはこれで十分に利いているので、会ではこれ以上捻らず、あとは伸び合いで離れるように。」