I can't speak to the insulin part of the question, but I was giving my cat only about 2 tablespoons of Evo and it was definitely impacting his BG. When I finally just cut it out completely his numbers dropped a whole bunch. Turns out he's super sensitive to carbs and even a "healthy" kibble was just too much for his little pancreas. I know there are people on here who feed it and don't seem to have any problem with it, but Sam sure did.
Another thing that made a difference was his litter. I was using a corn-based, clumping litter that was flushable. That means that if water/pee touched it, it would dissolve. It also means that every time he used the litter box (and diabetes made him use the litter box a LOT), he was getting corn on his paws, then ingesting it when he cleaned off his paws. Switched litter and his numbers also had a noticeable drop. Kind of the same thing on this one: I know there are people on here who use the same litter and say it's no problem at all, but it was for my cat. I think some kitties are just super sensitive, and I got one of those kitties.
Don't know if any of that applies to your situation at all, but I've noticed that little changes seemed to impact him a lot.