the physical properties of how the shelf is cut with regards to the centerline of the riser is extremely important when in conjunction with dynamic arrow spine. then add in the shooter's form consistency, or lack thereof.
This statement pretty much tells the whole story.
But.... in addition to this i think the bows limb design itself, brace height used, the type of string determining the efficiency rating, in concert with shelf cut out location can be a determining factor on spine selection too.
an extreme example would be a 50 pound recurve cut to 1/8" past center with a 16 strand string, and braced at 8.5" that shoots 170 fps.....
vs..... a long bow of the same weight cut to center using a 6 strand string, braced at 6", shooting 195 fps..... the long bow here can and will shoot the same weight arrow with a stiffer spine shaft with the same length and same point weight even though its only cut to center. The same thing applies to round wheels, vs energy cams in a compound bow....
The very cool part about carbon shafts is the recovery time is so much quicker.
I've always leaned on the side of tuning a more flexible shaft with the right point weight. I'm thinking that if you were to get a less than perfect release, the effect on the arrow flight wont be as extreme as a stiffer spine shaft.....
Any thoughts on that line of thinking guys?