that is why when a do the ball round house a aim for the soft partsI have been corrected by a Kyokushin guy regarding the instep to the skull. He explains that the force dissipates, unlike when you hit bone on bone to an elbow. So the foot usually doesn't break. Instep to the skull is perfectly fine in his words..
Having established that, is the reason you don't do instep breaking on wood that the force doesn't dissipate?
Also, how common is it for people to break their toes when failling their ball of their foot roundhouse?