Thanks for getting back.
I surmise that the coal hammer grip is a special class of grip that violates the previously established relationship between adduction and precision.
That said, if one takes the illustrated "power" grip and adduct the thumb only (not changing the fingers) until it touches (or almost touches) the forefinger, you have the 'nail-hammer' or 'fly-rod' grip. That is the top hand grip I use ... come to think of it, both hand grip, stacked, but not fists. The "knocking" knuckles of the top hand split the "punching" knuckles and the "knocking" knuckles of the bottom hand (whatever the name of that finger bone is.) But the fingers are 'smeared' along the handle as in the "power" grip vs. perpendicular to it as in the "coal hammer" grip.
Post a followup: