The focal point of the bareshaft method is not the nock end, but the point end...where the arrows strike the face of the target relative to your point of aim. Jim is correct, what you are trying to achieve is a pattern to inform the rest of your decisions about adding weight, reducing length, etc.
Hold the bow verticle and just remember that when you fletch the bare shaft it will stiffen the arrow. Thus, initial tuning should aim for a slightly weak shaft (3-4") When fletchings are applied, the arrow will no longer fly weak.
Claudia