If we can get a closeup of the Winterhalter painting you'd notice the remainder of the jewel does not look like any of the peices you've indicated on how it was worn by other Queens. I can't explain it but the original picture I saw can expand and one can clearly see a substantial attachment with the cockade sitting at the top or the head of the jewel. I'm going to try again to see if I can attach the picture here but I confess I don't know how too.

Regards,

Dave.