Bob, there are 2 reasons I can't give you exact measurements of quantity of the 3 oz of mixed chiles.
First, the chiles are used whole, as I said, not dried and ground into powder. Makes a huge difference in volume on the puree.
Secondly, the mixture I use is according to my own tastes, and the feedback gotten from folks who have tried my chili recipe. Your tastes may differ from my own. I know folks who have made the recipe using almost all chipotles, and they like their chili very hot! It's only after learning about the flavors of each individual chili that you can experiment and come up with your 'signature' mixture, in much the same way you devised the proportions of your dried mixture. Anchos taste different than guajillos, or pasilla, or chipotle, and it's only by tasting each one that you can get a true sense of what they're going to bring to a dish.
To me, that's what most cooking is about. With the exception of baking, which does require a basic formula to begin with, cooking is more of an alchemical experiment, where different ingredients and amounts can be added or taken away, once the 'basics' are learned.
To bring a comparison to the lab - any lab tech can take a prescribed 'method', apply it to his experiment, and get results. But it takes a true scientist to be able to interpret those results.