Its a separate piece of head gear, I think there are 3 or 4 variants depending on the style of Lance cap being worn at the time . Other ranks had a cover. I think someone at the Auction house saw the picture and assumed the plume fitted in a small hole. The whole point was to not let all the feathers and Melton get damaged in bad weather or battle and leave the parade one safe and sound in its tin. Which I also got named to Clerk..