Thanks for the feedback! In response to all of your questions:
The boxes currently have about 6 inches between them. I talked to the vet today and they recommended they be moved far apart.
Their sizes were described as large when I bought them in the store.
They are close to the washer and dryer but the washer and dryer just got hooked up and this was an issue prior to their use.
And I don't recall the boxes ever being cleaned using bleach. I was always under the impression that cats wanted to be able to smell their own scent so I decided not to clean the boxes too well. Other than some warm water and mild soap, the boxes have never been chemically disinfected.
We took him in for a checkup about 2 weeks after adoption. All was well then, but the vet did suggest that a UTI may be contributing.
The shelter only told us that he has a very small heart murmur. And when we took him to the vet, the vet nor the vet's assistant could detect the murmur using a stethoscope. One of the unique things about him though, is that his hair is quite long, even around his rear end. We've found a few "dingle-berries" and some other waste resin caught in the hair around his anus. Not sure if this plays a role or not.
The boxes are uncovered.
The litter is scented, both have odor control formulas.
Ozzie is a rather small cat. His long hair makes him look bigger than he really is. When you pick him up, he weighs less than 10 pounds and is quite flexible. Like I said, his long-hair feature makes him look much more hefty than he really is.
I have not removed the cardboard nor have I cleaned the area. I wanted to keep this problem contained to this area due to the fact that he is going on cardboard and not on my furniture, my living room floor or my carpets. What cleaner is the best to use for cat urine/feces odor?
I think the first thing I will do, and please offer some criticism if you can, is throw the cardboard away and move the litter boxes further apart. I want to clean the area around the boxes but I need some info on the correct cleaner to buy. I'll put some fresh cardboard down around each box in order to detect any future "target" misses. And this is difficult to admit, but I am going to apologize to him for rubbing his nose in his most recent urine pool :-( That was an old-wives trick that was passed on to me and according to this forum, is obviously outdated and cautioned against. Also, should I thoroughly clean all the boxes and distribute fresh litter boxes for their new locations in the basement? Thanks for all of your info! Tremendous insight!