I don't think that there has been any definitive analysis of wound channels with different meplats, but the concept is easy to understand.
First.... if you have a spitzer bullet which does not expand, like a FMJ, and it goes straight through without tumbling, you would expect that it will slip through the tissue with a minimum of destruction.
Then, if you had a round nose bullet which does not expand, it would go through tissue with a little more disruption of tissue than the non-expanding spitzer.
The next level might be a spitzer that expands into the classic 'mushroom' shape. Note, however, that the 'mushroom' shape really mimics the RN that doesn't expand, except that it might be much larger (1.5 or 2 times caliber, typically). So it increases the wound channel further still.
Curiously, a flat-nosed bullet, which does not expand, still makes a pretty good wound channel. This shows the value of different meplats. The very blunt nose crushes tissue, it can't slip through. The destroyed tissue is the permanent wound channel.
Throw some more confusion into the story, how about a shape that is different still, like the Barnes "X" or Win Fail Safe. Either of those two opens up into petals that are not going to slip through tissue easily. So their meplat value is harder to calculate than just measuring the expanded diameter of the bullet.
Last factor, what is happening to the tissue that isn't destroyed? There are shock waves going through the tissue as a result of the bullet. Slap your hand down on water and you'll see the same concept, tissue is mostly water. That is energy that is being released and sometimes that energy helps disrupt the central nervous system or vital organs, even if temporarily. Ever shot a deer in the neck and it dropped, then got back up? The nerves in the spine were temporarily disrupted, but not permanently destroyed.
One other complication is an expanding bullet normally loses pieces of the nose or core. Those pieces go off in tangents to the bullet path, and are causing their own shock waves and tissue/nerver/artery destruction. This is why a bullet that loses some weight is not a bad thing, and may increase the overall effectiveness, compared to a bullet with 100% weight retention. After all, even if that bullet exited, not all of it did, and the pieces that stayed in, left 100% of their kinetic energy in the animal.
OK... how about a simple example:
Take a steak out of the refrigerator.
Poke a sharp knife through it. Easy, and minimal tissue destruction.
Poke a fork through it. Harder, and more tissue distruption.
Poke something blunt, like a spoon through it. Much more difficult, and you will see that the spoon tears more of a hole.
Thoughts, anyone else?
