First, you are more in control that you would be if you were guessing what was happening. IMHO, he is bouncing big time. He dropped early, more than 50% by +2. It was a nice slow rise - sometimes they bounce right after the lowest number. It could be that the insulin petered out early, but I am betting on a bounce. Did you steer him with regular food or higher carb stuff? If higher carb, that can contribute to the higher number too.
Two choices. Continue with the 1.5 (if you can monitor the low point and make sure he doesn't drop too low) and figure he will eventually get used to the lower ranges and not bounce. Or drop down to 1.25 and see if
he nadirs later in the cycle.
The good news is that he was in beautiful numbers most of the day. The bad news is that they didn't last.
Does this make sense?