From all of my testing, I think the smaller size and shape of corners helps. If you look at the video, you see the corner matches from the flow of the water around, which is how we designed it. However, I think that is minor, compared to the fact that my new surf deck is completely smooth underneath. Even if the corners were round, I don't think it would have much impact, but the smooth understand is what is eliminating the turbulence.
Also, when I took the step off completely, I got a rooster tail that came up, and and was a hinderance to the rider. The new deck eliminates the rooster, while also not making turbulence.
Lastly, the notch does effect performance for a more surf style rider, especially when the rider uses the lip for launching or other tricks. The notch messes up the lip and/or the run up just before the lip, which definitely has an effect. Sometimes there is also the secondary lip, which you don't want, which will go away with more list, but you can't list over more, or the wake starts getting notched by the deck, which is the problem I was having. http://www.youtube.com/watch?v=JAhsy8vfKzs&fmt=22