I have never had a class that specifically dealt with altering "finger focus" like this. However, I have ALWAYS been told that grabbing or holding is done with strength in the pinky, index finger, and tegatana. In other words you squeeze with the pinky-side of the hand, and relax the index finger area.
This has been told to me about bokken as well as taijutsu.
I am sure you have heard this before as well, but I think it is interesting that the art (across more than one style in my experience) seems to be "aware" of what you have discovered, in some way. Although, not many people seem to have experimented with it first-hand as you did. It sounds like you have hit on something that is built into the art deep down--yet we mostly had not realized it. I look forward to playing with that, thanks!