You have been increasing by 0.5 units every six cycles. Keep doing that, as long as you are getting at least two tests per cycle, until you see some lower blues, at which point I might hold for eight cycles. Post back here when and if you get to 10 units, and we change the dosing strategy.
I second Sienne’s recommendation to get testing done for acromegaly and IAA. One in four diabetic kitties has acromegaly, so it's not uncommon. Knowing what we are dealing with may change dosing strategy as well.
As for Lev, are you seeing your cat respond to the shot with skin flinching or walking away, or other signs? I think if you get the tests done and one or both are positive, I would switch.