Did you just sand it, or actually lap it (as in, used a piece of float glass, or a definitively flat surface like a specifically machined block of metal)?
Simply sanding it will result in a shiny copper top, but may leave it an uneven surface. Lapping gives it a proper flat surface, which is much more important.
You may wish to lap (properly lap) your H100i block too. They're shiny, but not always flat.