I've wondered about these various hand positions and today after watching videos of Yamaguchi sensei doing tachiwaza but with a bokken in hand could this possibly be the answer.
We have many ways of offering our hands for katate dori. Besides the hanmi aspect and the height aspect of jodan, chudan and gedan, we also provide an alignment of the hands. 3 of which appear distinct.
1. Thumbs up fingers towards uke's throat/upper hara.
2. Thumbs down fingers towards uke's center/dantien.
3. Palms down/palms up.
I wonder if 1 is when we are imagining holding a ken or jo and if 2 is when we are drawing our weapon from the saya.
Some senseis have disdain on the palms up and down version and some have equal disdain for version 1. Each provide their own reasoning. One thing I've noticed however is that when we trained with weapons last night, it was easier for the beginners to find the chushin connection with uke. Even though we constantly remind ourselves to feel that when doing tachiwaza, it appears as if they totally lose the integrity of that thought without a weapon in hand.
Certainly when imagining the weapon in hand, the hand alignment is important with regards to what technique we are doing. It appears entirely inappropriate to cut up if our hands holding the imaginary weapon doesn't really allow for a realistic cut in that direction. Equally important is our ability to transfer our 'weapon' between hands to accomplish certain techniques. Visualising that really identifies each hand's unique role during the application of the technique. If say for example a sayo undo with a 'jo', we are using the alignment of the jo and our chushin to affect uke's center and not for example to sweep his head aside then the technique appears effortless. But a slight change in how we grasp the 'weapon' we could have our lower hands stab uke's center with a wakazashi and now the dynamic changes the sayo undo, it feels different but retains its effortless effectiveness.
Just a random thought of the day...