The deck opens along the inside edge and a pad of flesh on the pinky finger holds the two blocks of cards apart.
In this grip the hand hides 3 sides of the deck.
A portion of the skin on the palm of the hand holds the break here.
It is possible, while holding a fine pinky break, to bevel the cards.
The size of the jog should be proportionate to the squaredness of the deck.
Grasp the deck in the upper hand and allow the angle jogged card to clear the thumb.
From this position the pinky can either pull down to form a break above or push up to form a break below.
Notice only the pad of the finger is inserted. This style of break was popularized by Charlie Miller.
A proper finger break leaves no trace. The 2nd and 3rd fingers form a shield to hide where the deck splits.