I don't think you are missing anything at all, Angela. I think it is that #%£€ ECID thing. His body reacts the way it reacts, and clearly with Henry, unlike any other cat. You have spent a lot of time manipulating the schedule, the doses, the food. Things help for a while or once, and then he is off again. Raising and lowering the dose doesn't do what we think it "should".
I figure it is like any hormone/medicine. Some people react well to it from the beginning and it works great. Other people use the exact same stuff and it doesn't work nearly as well for them.
There is, of course, no guarantee that Levemir will get him OTJ. That would be the best outcome. My next best hope is that you could get him regulated, in decent numbers the majority of the time.