Ah, sorry, now I remember
I don't know if you're getting scented or not. If so, try an unscented clay. Sometimes their noses are sensitive to the perfumes. At least you'll be able to see if he's going.
I don't rememberr if you got him checked out by a vet or not, but if he seems to just not be ab le to make it to the litterbox, that might be a problem (one that can be fixed). Perhaps a bit of a urinary infection.
The amount he's going seems fine to me. They have very small digestive systems compared to us.
Do you leave food out for him all the time? If you're trying to have some control over when he goes so you can direct him to the litterbox, you might try feeding him instead several times a day just what he will eat and then remove it, then take him to the litterbox until he goes. He'll have to go less during other times if he's not eating constantly.
Also, how much traffic is there in yoiur house, and how much noise? Some cats really like privacy, like people do, and perhaps putting the litterbox(es) in places where there is some privacy (even if it means putting something in front of it for a while) might help. Maybe even taking a big carboard box, cutting a doorway on one side, and putting it upside down over the litter to make a little "house" if you don't have a place that would be out of the way. If that solution works, they sell these litterboxes that have covers over them already.
I once heard a situation where suddenly a cat stopped using the litterbox after it was scared by a noise from outside while it was going. It was suggested the owner keep the cat confined with the litterbox, but with supervision, so when the cat went they could talk to it gently and "untraumatize" it.
Just some ideas. Keep us up to date on what's happening.