As I mentioned, I wasn't happy with the over-thick flange on my original dome, so I made a new one using the "squashing on to a tube" technique that worked quite well for the chimney. Here we see the squashing stage in action, after drilling out and thinning the bottom flange.

The resulting dome has a much finer and more realistic flange, as well as a better cylindrical shape, as you can see in the following two comparisons:

Notice that the dome cracked around the bottom where it joined to the flange. I filled this with solder to arrive (after some careful filing and sanding of solder) at the following result: