I don't see anything wrong with the layout you are using.
I am building one 70 inches total (about 68 NTN), with an 7 1/2 inch handle section; center of handle will be 1 3/8, down to 1 1/8, back to 1 1/2. From that point (1 1/2) the limbs will taper to 1/2 inch tips. The length difference between top and bottom is a full 2 inches.
This is my first Torges style bow. I have a very long draw that has lead me to such a long first bow. I hope to try shorter bows (68 and 66) in the future.
If you are having problems with the taper, I suggest practicing on some scrap pieces. That's what I am doing. Hopefully, it will help me produce a workable first selfbow.
Dean does suggest reducing the limb offset as you move to shorter bows. Something you might want to try. I think he says he uses about 1 inch for bows less that 64 inches.
Good luck, and keep playing with the deminsions until you find one that works for you.
- Michael