I had a Russian Blue for 16 years that had a problem similar to what you are experiencing. I found one thing by trial and error, be consistent with your brand of litter. He hated anything that was heavily perfumed. I read not to long ago, that cat's do not know "automatically" how to use a litter box. Since Chanel (thought HE was a Girl) came from a breeder, I didn't really know how or if he was ever introduced to the litter box properly. This may have made a difference in my frustration of 16 years. I was never capable to get rid of him, I always thought he'd get over it. He would for awhile, but I always had to keep an eye on him. It's funny that all of the other cats I have ever had, (rescues) never had this problem. Best of luck to you!
CJ