Could the litter box I’m using just not be the right fit for my cat?

Yes. The box should be appropriate for your cat's size, age, and condition. Senior cats or cats with physical ailments might find a top-entry box or one with high sides difficult to use. These types of litter boxes could also pose a challenge for awkward, tiny kittens unable to navigate them well. On the other hand, if your cat is rather large, one with higher sides would be a smarter option.