Head on prone men are 10" disks as targets
not 20", and that is if ground swells and vegetation,etc, do not cover or conceal part of the enemy as he lays there. If you will remember your geometry, the area of a circle increases by the square of any increase in the radius, so the 20" circle is not just twice as big an area as the 10" circle, it is 4x as big. So stop kidding yourself by firing at 18"x24" torso targets, nobody is going to be standing erect and holdinig still while you shoot at them, and nobody is standing around after you fire a " spotter" shot, either. Once you fire one shot, the enemy will all be going prone, moving to cover, etc.