Just a FYI, I noticed on Feb 10th, you also got a number below 90, which would have meant reducing, but you were at 2.0 units then. ON Feb 15th, you increased by 0.5 units. If you are following SLGS, we do changes by 0.25 units at a time. I think Colby is telling you he really wants less insulin!
A question, can you get any spot checks at night, perhaps just before you go to bed? I know it's hard to get tests during the day due to work, but many cats go lower at night, and we determine how to change the dose based on lows, so getting some tests in at night is really helpful in figuring out what a dose is doing.
How is Colby feeling/behaving now that he's getting insulin? Cats are so much more that their numbers, which is all that we can see.