Official Luthiers Forum!

I understand that the depth near the neck will be shallower than the depth near the tail block, by a significant amount, but what about the depth between the two? Does it decrease at a steady rate, or is the taper from the neck block to, say, the waist steeper than that of the tail block to the waist?

It should be determined by the radius of your back, if you use one.
If you profile each back brace with a different radius, all bets are off. Older guitars tend to have a "flatter" side profile.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

It may just be a good idea for you to buy or borrow a couple of books and study some guitar plans. There is no "set formula", but I use the measurements from plans to set the height of the neck and tail blocks and then let a radius dish take care of what happens in between. It seems like there is quite a bit more taper between the waist and neck block...

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Don't confront me with my failures--I have not forgotten them.

Think about the geometry. If the top and back are flat, the tail block is (say) 4" tall, and the neck block 3" tall, then at a point halfway up the length of the body the sides will need to be 3-1/2" tall to preserve the flatness of the plates. If the back and top are domed, then you are looking at the intersection of a sphere with a guitar shape, which is going to be a pretty tough line to describe mathematically. It usually works out, on steel strings, for my guitars, that the side height is more or less constant (maybe even a little deeper just below the waist than at the tail, depending on the amount of taper), and most of the actual side taper happens in the upper bout. As Laurent says, except for the simplest case (which nobody builds, to my knowledge), the shape of the side is pretty complicated.