Moon,
You ask a great question, one that I've wrestled with as well. Here are some thoughts and certainly not the "definitive" answer on X-holes since I still have much to learn. After consideration, it seems to me that we are seeing a philosophical difference in approach.
Mo's gradient line approach is new and it is intended to complement the dual angle drilling technique. That said, I don't believe there is anything wrong with using his approach on any ball. We have used the dual angle technique with success in our shop. One thing to notice is that it keeps the x-hole in a safe location. by that I mean you will not run the risk of flaring over the hole which you could possibly do if you go too far beyond the VAL.
Brunswick recommends a much simpler approach for x-hole location. They recommend the hole be place 2 1/4 past the axis to increase flare. However, they correctly warn that such a placement may cause the ball to flare over the x-hole. They recommend a second position of 2 1/4 away from the axis but toward the pin as a flare decreasing position.
Generally speaking you need to decide whether or not you intend on shaping the core with the x-hole or if you just want to remove side weight. in order to affect the core you need to go at least 2.5 inches deep. Larger diameter and deeper holes will typically increase flare a bit more. By nicking the core you actually create asymmetry which will affect flare and the ball roll.
In terms of VAL, please keep in mind that this line really is just for the driller. By that I mean that it has nothing to do with where the ball rolls. It is just a reference line. In the shop I work in we typically will use the VAL as a location for the x-hole. The link below is an excellent video on basic x-hole effects. Nick has done a great job...you want to view "BVP Wizard X-Hole Demo".
http://brunsnick.com/faq.htmlRegards,
Fran
