Unless I misunderstood, Abernathy isn't out of remission -- he'd just been started on Prozinc and recently switched to Lantus. Is that correct?
Has anyone run through the difference between Lantus and Prozinc? If so, I'm sorry if this is redundant. It's helpful to always remember that Prozinc dose is largely based on the pre-shot numbers. Lantus dosing is based primarily on the nadir. (We look to the pre-shot to make sure it's safe to shoot but dose changes are based on the nadir.) Lantus is also a longer acting, depot-type of insulin. It takes several days (5 - 7) for the depot to form. Having the depot allows Lantus to act in a cumulative fashion and allows for overlap between the doses. This doesn't happen with Prozinc because while it is a longer acting insulin compared to many other types of insulin, it is not as long-acting as Lantus or Levemir nor does Prozinc have a depot.
The reason for my making the above points is that it's important to do what you can to get spot checks at various points during the cycle. It's the best way to keep your kitty safe and to make sure you don't miss a needed dose reduction. It's also important to note that not all cats have a nadir at +6. Some cats have early or late nadirs. (For example, my cat's nadir is typically at +3 or +4 -- except when it's not.) Nadirs are also not fixed points; they can change. (This is because cats like to be unpredictable and make us crazy.) So, testing only at pre-shot and +6 may not be giving you the whole story. Testing at various times will help you to understand when Lantus onset begins, when the nadir falls, and how much duration your getting.
I'm reticent to suggest that you drop the dose given the history of DKA. Has the infection cleared up? DKA typically results from an infection/inflammation, not enough insulin, and a cat that's not eating. I'd sooner see you feed Abernathy more or use some higher carb food until we know that ketones are a thing of the past. Are you testing for ketones?