Pretty much, a shorter or direct impact will have most fragments falling back to the planet. In the case of a grazing impact, the collision happens over a much longer duration, with fragments being throw off in each step.
Additionally fragment count is a level of detail controlled effect, if your computer is more powerful, more fragments will be created, until you hit your "cap".
I'm not really clear on what the issue is? I suppose the short answer is, yes, they are supposed to make as many fragments as they can.