I'm by no means an expert on this but this is my interpretation...
When you wrap a mesh up in a convex mesh its kind of like wrapping a model up in gift wrapping, so every detail is not going to be copied but the general shape is going to replicated. Also you have to remember that its a convex
mesh meaning that it will not have any...errr.. concave bits, you know like craters, recesses etc.
I have attached a piccy, to show you how one might be created around a model (the red is the convex mesh)
I know the voices aren't real, but they have good ideas!