I think the problem here might be the mesh its self, and perhaps also in the UV mapping. As I understsnd it (and I don't understand it very well) an object can only bend along seams in the mesh the more seams the smoother the bending. See the comparison between your figure and a Poser box prop when a magnet is applied, the boxprop has more places where it can bend.

I think whether the vertices are split or welded may also have an effect on how the object bends, I think welded vertices will will give a smother bend.

I an no expert on any of this, but hopefully someone with more knowledge on this subject will either confirm or deny what I have said above.