[quote=Skallagrim]
Asta is right, a punch and the power in a punch come from the correct stance and then technique and speed/power of hip rotation, shoulder thrust and correct delivery of fist.
[/quote]

All of that, correct stance, technique, hip rotation, shoulder thrust and rotation, and fist delivery, is designed to generate as much speed as possible on the smallest area possible. Strength is used to generate that speed, yes, but it has no effect on the actual force of the blow. Mass and velocity are the defining factors, and one need not be grounded in order to deliver kinetic energy to a target. Take bullets for instance. Shooting a guy in the chest with a .45 (who's wearing a bullet-proof vest) tends to knock him down (or at least stagger him) quite handily, as well as break or fracture ribs. The bullet doesn't have any connection to the ground to generate additional force, but it still has the majority of the momentum it left the barrel of the gun with. The same concept applies to Mifune. At the point when he leaves the ground, he's essentially a human-sized sub-sonic bullet. All that force isn't going to suddenly disappear when he hits Herriman. It's going to be transferred first to the protective shield (which based on Herriman's descriptions wouldn't be able to absorb all of it), then to Herriman's chitinous armor and, when that fails to shatter completely, back into Mifune's hand.

Honestly, there's no way the move ends well for Mifune. He just doesn't have the durability to withstand an impact at that velocity. Then again... neither does Herriman. It's just a matter of who breaks more first.