I've always gone with the idea its the amount of wood you have bending that determines how the bow will behave and not the dimensions of the bow itself. I have looked at pyramid bows and longbows of the same draw weight and the amount of wood that is moving is about the same and they take about the same kinda set. I bet if you made the bow a bit longer it would have taken less set and shot a bit faster too! Just my opinion though. But design does come into in where the wood is doing the bending as shown in BB Vo. IV. The holmalgaard bows and the the Eifal tower designs are good examples of this. Keeping the most amount of wood that does the bending closer to the handle and less at the tips makes for a faster designed bow.
Hmmm! I wonder what happens if you make a bow equal width for its entire length that bends equally everywhere along its length if it will be a fast bow or not? Man, the more I learn about bows the more I learn I don't know about bows!!!!