Gozo Shioda says in one of his textbooks that the hand should be open with the fingers apart "like a Morning Glory flower". This is (perhaps not surprisingly) what Kanetsuka Sensei teaches too. All the Aikikai shihan I have seen keep the fingers open.
I don't think I have seen anyone demonstrating with the fingers together. Are there any examples on YouTube of this?
The concept of the fingers being spread in relation to the Morning Glory flower has also been quoted by Chiba Sensei. Chiba Sensei indicates that in the evening the flower closes down its foliage and when the sun/light returns the flower opens up its petals.The fingers as you know are not tense.On a personal note I train my own fingers to open [and my Kokyu flowswell] when I hold a pint of fine quality beer.No need for me to go into any metaphysical /supernatural explanations when I am in form at the local tavern.Might be in your neck of the woods this year -my grandson is training as a Marine Cadet [Merchant Navy ] in your area. Cheers, Joe