Mine do this too, what helped with Tucker was adding an extra tray..she’d then use one for sitting in and the other for her actual litter box. This way I didn’t worry about her sitting in a yucky litter box and once she got in the habit of not pooping in the one I used some of the carefresh that I use for the hamster cage in her sitting box so it was nice and comfy for her
Now that Drue and her share a space I’ve found that they’re doing the same thing..unfortunately they’re now using the LITTLE box as the pee/poop box and the big HUGE one as their sitting box..I’m going to try changing the location of the two to see if that helps LOL
Oh and my hamster kind of does this too lol..but she seems to use her litter box as a full on powder room. Every evening she wakes up and stretches, go gets some water from her bottle and then runs over to her litter box in the corner and she preens herself, pees and poops and then goes upstairs to her lookout tower which is where we feed her..it’s just amazing how they have their littler routines 