The asymetric shape is debatable as far as how good it really is or even necessary.

You want to have the longer part of the blade on top. The reason is, because you are up in the air and the paddle is entering the water on an angle, so in essence, the asemetrical shape is makingthe the blade have equal resistance rather than favoring the bottom which would have greater length because of this angle and thus cause a bit of twist. If you were sitting in neck deep water and paddling underwater with the paddle straight out from your sides, the asymetrical blade would not be necessary. I've paddled all types of blades and find no real difference or advantages of one over the other. It's kind of a fad in paddlemaking by manufacturers. Derek Hutchinson (noted expert on everything) sells a symetrical paddle and points out it's advantages etc. Manufacturers have every blade shape and shaft shape imaginable. With experience you'll find what feels good to you. But it's the longer part on top.