[unboggling]

If you mean format-specific metadata elements that you want to enter/edit then see displayed in the Library View booklist (or on a metadata jacket inserted into the format), this is what I do:

Have a custom column (comma separated tags) that is for format-level tags only.

Dealing with format-level tags in a book-level row requires rules to avoid confusion. My rule: after processing the new book into calibre, there can be only one master format for that book. No other formats are allowed for that book unless there is good reason, such as automatic-convert of master format to different format to read on specific device. Master format stays. Any other formats get removed during initial processing or immediately after temporary use.

With that rule, all my format-level tags act as if they are book-level tags, and they like it. That promotion in levels makes them feel less looked-down-at and more useful.

If I had to keep multiple formats per book for some reason, then in my format-level custom column I would enter format tags like this:

AZW3.good, EPUB.good, MOBI.problems, ...