You ARE a rocket scientist aren't you?
I have to give your due, You have tried to answer the 64 million dollar question and done a good job of it too.
The Zahn cup is a nice tool but can get you into big trouble as you've (I hope) realized. Reduction is a good thing but like booze need's moderation and common sense.
I used one a few times but ended up just staying within the Manuf's guidelines for the product for the most part and had much sucess doing so.
It just got to be TOO much measuring and fiddling around.I just want to paint.
Glad you got what your looking for.