Melting cheese/chocolate

Why do some things like cheese and chocolate melt better (i.e.: faster and more completely) if they are coarsely chopped instead of finely grated? This seems to be true and is counter-intuitive to me.

I don't really know but I always use a much lower heat for grated cheese and chocolate and am not so careful with the heat when the pieces are bigger.

Maybe because cheese and chocolate conduct heat better than air? If you have a big lump of chocolate, the surface that's in contact with the pan will conduct the heat through the whole lump of chocolate. If the chocolate is finely shredded, a lot of it is completely surrounded by air.

-Paul W.

We always use a double boiler for both; and it isn't important how you prepare them first.