question on Dynamic Spine and long insert

[sbschindler]

I have a question about the longer 100 grain brass insert and stu Millers dynamic spine calculator and arrow lenght, the general opinion is that the longer insert stiffens the shaft, well ok when i put in the length of the arrrow should I put in the length of the arrow to the back of the insert and not the point, I know that the common belief is the back of point but thinking outside the box maybe back of insert would give better info ????????