The quick answer to your question is, "Yes." Having Mr. Grey in the 120 range at pre-shot and nadirs mid- to -upper greens is fine.
That said, it all depends on what your goals are. If you are wanting to keep him tightly regulated, this is a perfect scenario. He's in normal numbers. You have the latitude to go up even a bit higher but ideally, keeping him in a normal range is good for him. As long as he's below renal threshold (200 - 220 -- it varies depending on the cat) there limited risk for organ damage.
If you are hoping for remission, then you will need to increase the dose. The challenging piece here is not knowing whether Mr. G. is an acro kitty. I'm personally leaning toward his being insulin resistant and that you've broken the resistance. When this happens, the cat is pretty much like any diabetic cat and you can follow the TR protocol. If he's acro, you need to be cognizant of whether growth hormone levels are rising and adjust doses in accord with what the hormone is doing.