Whether your thumb and forefinger touch is really not important because that would depend on the size and shape of the grip and the size/length of your fingers.
What I do think is important is that your fingers are relaxed to the back of the grip so the bow is already "caught." This does two things. First, it relaxes your forearm muscles and allows better (non-interfered with by muscle) bone on bone contact. Second, you have already caught the bow which removes any unnecessary movement as the release happens.
Lastly, IF you CAN don't allow the bow grip to touch or pass your lifeline to the little finger side. That keeps the center of pressure of the bow on the base of your thumb and directly on the end of the arm bone behind the thumb.
Arne