Also, how the BG curve goes can be really specific to the individual cat and also depends on the type of insulin you're using, and how and what you're feeding (wet low carb food only? is there any dry? does your kitty have access all day to the food? and is there anything else he could be getting into like dog food? (my cat does this!)......
For instance, I notice with my cat that if I'm giving snacks of fish rather than low carb kitty food, her BG level stays much more constant, with the little bit of carbs (tablespoon of Fancy Feast classic) it causes a noticeable spike in her BG. She's on lantus and the spreadsheet is attached if it's helpful for you to look at the values I'm getting for her.