Hi Gary,
I also have a couple of these low pedestal plates such as yours, although mine are 12" in diameter and 2 1/4" tall. A long-time Club member and Flow Blue expert from England told me that they are probably the base for a covered cheese dish/dome (I think she called them Stillson domed cheese keeps). That is, cheese would sit on the pedestal plate with a matching dome/cover on it. It could also just be used open as a serving piece for cakes, sandwiches, etc. Since you don't have the dome/cover, you might want to just get a clear glass cover of some sort that will sit on it. Anyway, you have something that is not very common to find. Congrats!
Jon