so the covers i design will be quite good then big convection slots top and bottomThat's exactly how I understood it, stem.
Which is why I asked the question - most covers I've seen don't have significant openings at the base to allow the entry of air and even fewer have openings at the top to allow the heated air to convect directly upwards into the room as the radiator is intended to function.
Unfortunately, I fear that the main purpose of these covers is to keep as much of the rad as possible enclosed and out of site, and that one with a significant top opening wouldn't be acceptable for aesthetic reasons...
After all, you wouldn't be able to put ornaments and flowers and stuff on the top then, would you?
and very open front