Wow, Amy...you are quite the scientist! One of my cats will once in awhile choose to not use the box. I will keep this product in mind.
Speaking of cat litter, I recently got a free jug of Petco's own litter with a purchase of Royal Canin cat food. The last time I changed the litter, I broke this stuff out, and I really like it! It really absorbs the moisture out of the pee, so the clumps are nice and hard, without contaminating the rest of the litter, so to speak. I think I am switching to this brand permanently from Tidy Cats. The messes scoop out so clean and the rest of the litter stays unaffected. With Tidy Cats, many times the rest of the litter gets nasty pretty quickly.