We have two cats, and two boxes. They are covered (because PJ has peeing over the side issues), and they are gigantic. We also use LOTS of litter, and probably change out the pan itself every month, and scrub out the tops since sometimes PJ's pee will end up on the back.
They don't seem to care at all about any type of smell in the box (it doesn't really smell, we mix baking soda with the fine tidy cats litter); it's if there's stuff in there, Teddy gets annoyed. Usually he'll wait until right after I scoop it clean to go do his thing. We scoop 3-4 times a day, however many times it needs it. Whenever there's something in there, unless it's freshly put there, we scoop it. Nothing sits in the box for long if we're home.