Well, I haven't made this yet but it's on my to do list, but having looked at the pepakura model I'm assuming that it would be a straight line from arm pit to arm pit seeing as the chest piece itself fits around the base of the arms, and the shoulder bells etc are a seperate piece. One thing to take into account is that you need to make it a straight line distance as that is what Pepakura Designer uses when you measure Point to Point, it doesn't take into account the curvature of a chest etc which increases the distance.