Kibble size meant to clean teeth is geared more towards dogs than cats. Dogs have grinding molars for crushing, your cat does not. Forcing a cat to chew a food usually causes more plaque not less. Your cat’s teeth are like little ice picks and when you chop ice only the point stays shiny. It is the same with your cat's teeth. The problem area is at the gum line and that never gets scraped. Many small particles of food become lodged between the teeth and gums, when pointed teeth chew a hard food. Lodged food will increase plaque and gingivitis.
Cats prefer a food small enough to swallow whole and they like it roundish. Even if you give a cat a small piece of meat they will shake it and do the alligator chug and swallow it whole. Imagine chewing hard food on your eye teeth and all your cat's teeth are pointed. The optimum sized kibble for the average cat, is about the size of the pink eraser on a standard pencil.
The beauty of your cat not chewing their food is their teeth never really get dirty or have food particles lodged between their teeth. No dirty teeth means you will have a fraction of the plaque buildup and your cat’s dental checks ups will be better.
Bottom line your cat's teeth were meant for tearing and piercing and were never meant for chewing.