OK, I was afraid this might happen. In short, I do think that you need to taper the front faster to a much thinner shape. The top to bottom, depth, is great.
Now, if you feel a need to be bored to sleep, here is the long answer.
The fact that Whiggley swims without a swim lip or swim bill or surface is the key, in my opinion.
When water flows across the front of an object, it creates vortices or swirling water along the sides. The vortices start equal on both sides, but soon micro-imperfections cause the vortices to shift and eventually alternate, causing the Whiggley, or several different swim baits, to swim. The vortices get larger as they go farther from the front of the object so if you don't get the lure flexible enough it won't start to "swim" until further back in the lure. Also, the faster you move it the larger the vortices, so moving it faster will cause more "swim". Your lure seems to respond just as suggested.
I did some research some time ago to see if I could optimize that turbulence and to be honest I am not close yet. I did how ever find some interesting information.
If I understand it correctly, the first vortices is actually really close to the front. This explains why the hook needs to be far forward and why you need to have softer plastic in the rear. If the hook is too far back it stiffens the plastic and stops the vortices from working. If the plastic is too stiff, it also stops the vortices from forming.
So, what makes the plastic too stiff to flex easily enough? Several things actually. In Engineering, we would say that the shape matters a lot, the physical properties also matter. An example would be a fishing rod. In the old days, fishing rods were solid. They found out that they did not need to have solid rods but hollow rods would work great. In fact, for less weight, a bigger diameter rod could be made that was actually stronger and stiffer. The shape, hollow verses solid, mattered. Another example is the physical materials; graphite was lighter and stiffer then fiberglass. Material matters.
For the Whggley, as discussed, the softest plastic is best, as long as it is not so soft that it fails. This is the physical property part of the equation. The shape part is that the thicker the plastic, the stiffer it is.
I suspect that if you taper the Whiggley much faster, really thinning it down at the front, and then use the 2:1 softener ratio talked about, it will work very well.
Sorry for the long write up, and I hope it makes sense.
Steve