It does not matter so much where you measure the stack from as long as you measure on the same point on the bow you build. I would recommend you measure about 1/2" past where your fade out ends.
I would also measure at that point and then measure at the tips just before the overlays. If that number is smaller than you first number you will know what directions the tapers are going. You can also then figure out the taper rate by subtracting the 2 numbers and dividing by the distance they are apart.
This needs to be done very accurately with some calipers if you have them. I would then get in contact with Kennym when he gets back and he can help you decide what thickness of glass to use and the thickness of the tapers and parallels to reach you desired stack.
You also need to remember when ordering tapers that if you fadeout is 10" long and you measure the stack at the end of the fadeout, lets say you want your taper to be .100" at that point, you will need to order a taper with a butt thickness of .120" for a .002/" taper or .110" for a .001/" taper.
Hope this helps and keep us posted with pictures.