This is a simple and effective way to open up / fold the backs of the cover plates.

It may be more interesting to modify the back of the cover a different way, though. Some versions of the pre-war Marine Band had a much smaller "lip" but because of the 90 degree angle, it can provide a lot of support against crushing. It's still very open.

This is a modern cover plate modified in that way:

This is how it looks assembled: