I've got the beginnings of a watch case but, as of yet, no dial that I'm prepared to drill a hole in. I'm not going to put a hole into the cloisonné enamel frog!
My starting point is to create domed dials, this is because enamel miniatures typically require several firings and a domed dial will minimize warping. From fitting into the watch point of view, a flat dial would be easier but in the long term a domed dial will far superior for enamelling applications.
Warping is less of a problem for cloisonne (although still an issue) since the wires and counter-enamelling give the piece a greater thickness and structure that help to control warpage. However, I found a domed surface gives more interesting light reflections, it's more difficult to bend the wires over a domed surface but I got plenty of practice when I made these set of enamel doorknobs.