I wonder if the extension was ever used as a base for the tiara?

So far, despite extensive searching, I have not seen a photo of the tiara being worn with the extension as a base.

I suppose that, while it might seem feasible, it would depend on whether the original frame (or any later one) had the ability to have the extension fitted as a base piece. It is one of those mysteries which can only be solved by an examination of the frame or by seeing the tiara worn with the extension as a base.