Re: Fingers spread or together?
It is absolutely fascinating that the discussion is revolving around questions of which static position of the hand/finger complex is "correct" and almost no attention is being paid to the question of dynamic transitions between the three "static" positions of 1. Open and extended 2. Naturally relaxed and 3. Closed (either in fist or tegatana). This strikes me as being about as useful as a discussion on the subject: "Sleeping or waking, which one should you do all the time?"
Let me suggest some other questions that may be more useful:
How do you get from one to the other? Which ways of doing so are optimal and which are suboptimal? What is the effect of such transitions, on either one's partner or oneself? Why (or in what circumstance) is one better than the alternatives? This is not an exhaustive list of the dynamic possibilities, but it's a start.
Hope this is helpful.