Hi Cathy,
I bake a lot of biscotti and the recipe has a lot to do with the shape. Try comparing a recipe for a regular cookie that is more cake like to a cookie that isn't. Since I cut back on the sugar and don't use butter mine tend to be tight flat little loaves. Butter makes the finished product tender, sugar makes it "flow" and baking soda helps with the rising. It also makes a difference how much air you can get in the dough when mixing. I'm sure that bakeries don't mix the batch by hand like I do. I also make my ends as square as I can so those slices are as close to the same size and shape as every other slice.

Hope this helps,
Julie