There is NO void between the bottom of the spine and the top of the lungs.

In fact on a totally broadside shot the lungs are actually a bit higher than the bottom of the spine. (due to the upward curve of the ribs)

Many people do not realize how far down the spine really in the chest of a deer. I believe most people who think they hit a 'void' are really shooting OVER the spine. There is nothing vital over the spine, just meat and the spinous processes.

You know those hunting videos where the bucks are walking around with the little bald spots on their backs? That's the result of an over-the-spine shot.