A four inch penetration in the back, or front is nothing to sneer at.
Depending on the build, and where in the back it hit, four inches could reach the lungs, from the back, destroy a kidney, or other organs, and paralyze from the entry wound down,etc.
I would guess he used a target point, and not target field point, the ones that taper to a point. Good thing it was not a broad head.
Or obsidian........
Mr. Wood reminds me of the story of Paul Revere. ......a little light in the belfry........
Wayne