Not being the sharpest tool in the shed what I am saying is to be taken with a large grain of salt.
A parabola is a shape obtained by dissecting a cone with a plane. 1/2 of a parabola is a decreasing radius curve.
A parabola will have a very long radius curve starting at the one end, and then decrease the radius (Tighten the curve, or make it sharper to the point where the ray of the curve is at 90 degrees to the original ray. At that point the radius of the curve begins increasing in exactly the same proportions as before.
Looking at it this way it tells me that a bow that is tillered in this fashion barely use the working part of the limb and puts most of the flex in the limb tip. This is something that I shy away from.
I am basing this on my understanding of the shape of a parabola. Is parabolic tiller a totally different shape than what I am imagining? Please help me understand.