Basically halfway between the first and second knuckle will be where the gripping edge of the hole or insert will be on a finger tip drilled ball. Measuring the span in this manner is not new.

I guess all my stuff is wrong because it was measured from the first knuckle, I appreciate the replies so quickly.

You could do that, since your pitches will likely need to be changed. If you're that long, you more than likely have excessive reverse pitch in the thumb.

Is the semi-finger tip (relaxed) a factor in enabling these younger bowlers to create the rev rate that they do? Or is it simply easier on their hand after years of bowling?

Back in my formulative days of bowling, I was taught it was an option once full finger tip became too tiring or painful, and for others (though not many) simply a grip of choice.

Avabob summed up the history of the fingertip grip , as well as the effect of going to a shorter span nicely. In the 1980's, the "power release" was indeed much easier to do with a cupped wrist , kept firm at release, coupled with a shorter span. Mark Roth perhaps exemplified this release the best. He accomplished this while still maintaining
square shoulders throughout his approach as well. Today's power release is altogether a different animal. it's one that is accomplished by completely UNCUPPING the wrist (collapsing the wrist) backwards at release. It is also best accomplished by incorporating
an open shoulder on the next-to-the-last step as well as utilizing MUCH more lateral
spine tilt than the power release of the 80's. In fact, such extreme lateral tilt in the 80's
(by the power players of that era) would have resulted in a ball released with way too
much axis tilt since in those days, power came from the FINGERTIPS and not the
result of the fingers rolling up and over the circumference of the ball, as is the case with the collapsed wrist you see so much of with today's power players.

I still have a few students who utilize the 80's style power release. Many of them
get into trouble trying to incorporate the lateral spine tilts used by today's wrist collapsers.