Directly from Howard Hill on his description of the proper grip:
"you will note your thumb joint will be directly out from the center of the belly of the bow (See Illustrations)." - Howard Hill
Every illustration and existing photograph I've seen shows Howard Hill using the exact same grip as he describes above. This is taught by Wesley, is the way you'd naturally grip a suitcase, and is the way you'd naturally grip a pistol. This aligns your wrist and maximizes natural bone support. Hill was very specific to note the "thumb joint" and not the knuckle.
Howard had it figured out extremely well. Grab a straight handle Hill bow exactly as Howard described with the bow hanging from your side(pic). Experiment with the following:
First, Loosen the fingers in your grip and you will notice that the tip of the lower limb, pointed to the rear, will lower to the ground so that the bow is no longer parallel to the ground. With loose fingers, you will maintain good contact with the thumb and index finger around the top of the straight grip, but the lower part of the grip will pull away from the heel of your hand because the bow's center (balance point) is lower on the grip. Now, tighten the grip with your lower fingers and notice how the bow handle pulls up into the heel of your grip and the bow is now balanced and horizontal to the ground. Getting the bow into the heel of the hand is important as this centers your grip within the balance point of the bow. I'm of the opinion that some of the handshock felt and complained about is actually user enhanced (induced) as a result of NOT getting the heel down when shooting the straight grip. Without getting the heel down, you are choking your grip up above center causing the limbs to return out of time. This will greatly increase vibration felt throughout the grip.
The above Hill teachings aligns the bones of the wrist making for a solid bow hand directly behind the bows center.
There is an old target trick for shooting lighter Hill bows where you shoot the bow more like a locator grip by choking the bow with your thumb and top fingers while tucking your bottom finger(s) between the bow handle and your grip to fill the void. This works as you are using your bottom finger(s) to artificially create a locator grip and you are keeping pressure on the handle at the heel of your hand. But in my opinion, this is a poor technique to use for hunting.
If I may pass on some added advice, it is very important that you keep your bow shoulder down and back to prevent long term shoulder injuries. If you pay attention, you'll notice posted pics and videos of archers who demonstrate techniques that highlight Hill form, with the exception, the bow is of such weight that the shoulder is forced up and is compressed while at full draw, or the shoulder is not down and back into the socket as a means to increase draw length. Such technique is proven to place an archer on the fast track towards impingement and long term injuries. Keep your bow shoulder down and back or you may very well reduce the number of years that you can shoot a bow if you live to get old.
Best