Scratching a lot in the the litter box

Welcome!!
I have a question. Two of my cats go crazy in the litter boxes, they scratch everything from the walls to the floor to eventually the litter. And they keep going back to try and cover it when it's already covered. I've tried adding more/less litter to the boxes to try and figure out what would make them happy. Is there anything you can suggest about this or are my cats just quirky?
Thanks!

Yes...
first of all the majority of commercial cat boxes are too small. Instead of standard cat boxes, I recommend the 66 qt. Sterlite Clearview storage containers with no lid. They are really tall, which makes cleanup easier for you, they are large and a cat can see through them.
Also, make sure the litter is always scooped and somewhere around 2 inches deep.
Marilyn Krieger, CCBC