Jeremy, You are asking questions and thinking. That is a very smart thing to do when considering making these or any tools.
Your ideas of gentle taper are based on logic and solid thinking. An axe or hawk is not a hammer, so it don't need to be shaped like one or as heavy as one. In fact, it will perform better and look much better the way you have them visioned.
The human body is not parallel. The arms and legs are tapered to allow and follow principles of function.
Imagine a fine, top of the line tool of any purpose. A Bow is a good example. Then picture a cheap, crude knock off of that same tool, where taper, weight distribution, and appearance has been thrust aside to save some of the cost of production. It's easy to see right away when you hold it in your hand.
Just allow material for all of the parts, poll, eye walls, blade length(4 inches or so), and taper. Look at the ones you like and imitate those as close as you can or improve on the ones you have available. "Proportion" plus "Purpose" should be your guide.