Sounds frustrating for sure!
I would try doing it earlier, maybe once that double down arrow shows up even if he’s still high, and if you do it significantly earlier, you can consider a mix of carbs and protein (rather than fast acting carbs) which will give the carbs more staying power. Again, your risk will be he will end up a little high when he lands if he didn’t need it or as much, but that should be a relatively easier thing to tweak/less stubborn high.
And yeah, if he’s slim and active, I wouldn’t worry about the calories/carbs now—he probably needs them to go along with that growth hormone!