I've been largely avoiding this one.
But I'll chime in on some physics regarding what a shaped charge is.
A shaped charge operates because of (and brace yourself here!) the shape of the charge.
No really.
They were invented/discovered in the mining industry. It is unknown how long the effect was known to certain blue-collar miners; but an mining engineer took notice in the early part of the 20th Century. He noticed that miners were essentially etching metal with small plastic charges as a "Hey yall, watch this!" kind of thing and etching a reverse of the name of the company into the metal. The engineer went about finding out why. Turns out, it was the dent caused by the ridged name on the metal tin that plastic charge was shipped in that created a mini-shaped charge. It created a concave dent in the charge which, when detonated, focused the blast to the focal point of the concave curvature.
Think lenses and optics... but using explosive force instead of light.
This quickly got refined for military use. Particularly by Zee Germans. For those that remember their history, they were up to some shenanigans back around 1936 or so. The first big use of a shaped charge was with the Panzerfaust 30. A single shot infantry anti-tank rocket. Zee Germans had tested and experimented to find the most efficient conical shape to use.
The material behind the shaped charge really has no bearing nor does it really add any real confining force/pressure that acts to direct the blast. Mathematically, it is sure to add some; but of such a magnitude that it would not be included in any actually design modeling that one would carry out. I'm not going to go into the physics of this for sake of brevity; but that wouldn't work in this situation anyway.
What you have with a fragmentation grenade is a charge that is purposefully shaped to project metal shrapnel in all directions. It is omni-directional. In close proximity, the force of the explosion is quite intense and will cause massive damage to a human body. But, even a mythically tough hand is not going to "shape" the explosion back into the target. At best, the Mythically strong hand will simply match and/or counter the force that is imparted in the hand's direction with some leaking out around the edges of the hand.
How big is that hand anyway?
I honestly can not see a means by which punching someone with a hand grenade would generate any additional damage beyond the damage of the punch itself. At least in terms of real world physics. You mileage may vary depending on how "cool" and/or cinematic you wish your game to be.