The weapon was short, as shown by the reconstruction diagram. Having fixed the position of the attacker and knowing the position of the victim's head, the length of arc is exactly what would be true of a man's arm wielding a weapon less than one foot in length, i.e. about 36 inches in total. Naturally, the torso and arm lengths influence weapon length calculation, because the distance that can be established is the sum of the arm and weapon length. Even with a short arm, the length of 1 foot covers the available and necessary distance.
Paul L. Kirk investigation, forensic testing, bedroom