glass vs core ratio

[mcbowguy]

I've read from many guys that in a longbow a 20-25% glass to core ratio is considered optimal for performance and to avoid any significant limb set.  My question is what is the core considered?  The glass is easy.  It is a constant number of either .040 or .050 glass belly and back or whatever your combination may be.  Your core changes if you use tapered laminations.  My overall stack at the fade is .490 thick but is .386 at the nock (.004 taper per inch on a 68" bow).  Do I base it on the number at the fade or could you take an average by adding the thickness at fade and tip and divide by two and go with that number?

[Bowjunkie]

Stack thickness and/or core thickness is measured at the thickest point, usually the bow's center.... where the butt ends of spliced lams meet.