For years I have always measured FOC using the full length of the arrow plus broadhead. The shorter broadhead will slightly change FOC, but not much at all. The weight of the broadhead will change FOC more. Since I have gone to a shorter, smaller broadhead my FOC slightly decreased but is still within the range I feel comfortable with. And I am not going to change broadheads simply because my FOC slightly changed.....especially when I have had such good success with it.