Thought of something else to try to help, Greg.

Take a mech out and measure from where the point is closed up all the way like it would be flight. Now slowly push it forward, pulling the blades out as you push. How long does the shaft travel forward while leveraging your blades open? That would be your distance. But, keep in mind, while the blades are moved into a "trailing position," they are still left behind, so to speak, to cut at the beginning of the entrance hole. In other words, just because the ferrule has moved past the entrance point, the blades are now behind where they were and cutting back at the entrance point.

Of course, in this example, I'm using a rear-opening mech as an example, such as a Spitfire, Wasp, or Rocket.

That's what I'm sitting here trying to visualize; in reality, I've got to agree with Rack-Attack. All of my animals I've ever shot with Rockets have full-width entry holes -- including soft tissue matter like a turkey neck. That one was ugly!