Yes it is on the outside of the arm , right arm against right arm or left against left. Depending on how committed he is on hitting you , all you really have to do is hold your fist out and he will run into it with his face.
Just like mook jong said, this type of power comes from the loosening and elasticity of the thrown strike. The looser you are the more acceleration and power your strikes will have. You also need this type of loose movement to be pliable and adaptable to on coming forces.
