stubborn cat, help please!

I've read many similar posts so apologies for the repeat but I'm at my wits end. I've had my LR4 for about a month now and one of my cats has taken to it no problem, but the other one will use it once and then the next time she goes on the couch or the bed or a similarly annoying spot.

I've tried: - setting it up and leaving it off with litter inside to acclimate them - treats and affection while it's cycling - old litter box alongside - let the old one get dirty - cat attractant in the litter - waste from old litter box migrated to LR4 - praise for investigation of the LR4 - crying

I haven't yet swapped out the carbon odor filter and something I have noticed is that the drawer underneath smells pretty rank as it fills, even with a bag lining. With the manual box I was using a Litter Genie and it was always pretty odor-free. Maybe a smell problem? I also saw recommendations for the ramp, are folks finding that to be a game changer?

I'll go 5 days with no accidents and happy cats and then random poop on the couch or pee on the floor. Any ideas or suggestions are extremely welcome!