the "windows can cover" panel visibility mode seems to have been eliminated in plasma 6. i find that ... very unfortunate. please bring it back. i guess the "dodge windows" mode was supposed to kind of replace it, but i don't find that mode pleasant at all - it's "jumpy", and it's counter-productive to hide the entire panel when it would be only partially occluded.
*** This bug has been marked as a duplicate of bug 486701 ***