I have a couple of these too but I removed that top part sides are high enough for them. With lower sides my girls would often pee outside the boxes.
I also have one sifter box and it is quite good too, saves me one midweek cleaning and some wood pellets. Only it's a bit too expensive for me as I have too many rabbits.
This one, I removed that top part as well it's high enough
https://www.amazon.co.uk/4-Pets-Sco...ocphy=1007850&hvtargid=pla-564909958276&psc=1
It's not designed for wood pellets so they stuck in that yellow part but it's okay