Hels, there was a brief reference to this in a recent BTM, I'll dig it out and send you the info.
As far as I understand it, "tucking the pinky" is the next logical step from positioning of the "outriggers". If we take the extremes of position of the outriggers, there are four options, which I shall attempt to illustrate: here goes...
|oo| |oo/ \oo| \oo/
where the far left is least hook, generally and the far right is most hook (or potential as there is more "control" of the ball)
Tucking the pinky will increase the stiffness in your hand and therefore prevent any backwards motion of the wrist during the backswing, this increases leverage at release. If you'll pardon the extra comment, the reason your hand is on top of it is because your fingers don't always stay under the ball anyway, and this technique is going to exaggerate the impact.
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Reporting from England