I think that the proportions of the forestock are dependent upon more things than a ratio, at least in the initial stages of shaping them. The thickness of the web, the diameter of the barrel and how much of it is exposed, the size of the ramrod you choose, all play a role in how the forend will end up. And how it ends up is how it is...it's not something you organize and plan while the stock is still square.
I understand why folks might want a formula ahead of the shaping, so that they feel like they are less likely to make an error, or ruin the stock. Authors of "How to" books often offer advice on proportions so the builder is reassured that he is less likely to screw it up. But to me that is like trying to describe how to sharpen a pencil...Oh man, what happens if I get the cuts too deep, or not enough taper, or too close to the point. This is going to be a disaster. I can't do this!
If a builder is feeling these kinds of pangs, he needs to slow down and make smaller cuts and changes, progressing along more and more until he starts to see something he likes. Your rifle build doesn't have to be a three day rifle. This site has a plethora of knowledgeable and generous expert builders who are happy to offer constructive criticism of your work, gently steering you toward your goal. But I like to point out that you have to make those first baby steps yourself...go out on the limb and test it's supportiveness. Take a chance. Enough philosophy already.
