Arriving here in LB&L Land when a kitty and CG are starting from ground zero is rough enough. There is a big learning curve.
Arriving here in crisis, as you and Ming did - insulin transition gone wrong, flirting with DKA, numbers and dosing all over the place - that adds up to an initiation by fire.
With his recent history of ketones, having enough insulin on board is critical to keeping them at bay. Along with addressing any infections or inflammation, close attention must be paid to the balance of insulin and food. He needs his calories and they need insulin to convert the food to energy to be transported to and used by all the cells in his body. Otherwise his body will start breaking down its own fat and protein to fulfill the need for more metabolic energy and the downward spiral begins.
Most kitties that show up at the FDMB find the right dose by working up the dosing ladder. In Mings case its reversed - you are trying to find the right dose while going down the dosing ladder and with ketones still visible in the rear view mirror. You dont want a dose so high that he bottoms out at the same time you dont want to reduce at a rate and/or to a point where you open the door to ketones forming.
So feeding a level of carbs that will make for the smoothest possible decent to the right insulin dose is the strategy. Enough carbs so that he doesn't bottom out and then bounce to the stratosphere, but not so many that he ends up in a state of high carb hangover. Know what I mean? Right now 4% and under are not enough.
Try different combinations until you find the one that works best. There must be some way to figure out what, as an example 1oz of 4% combined with 1oz of 15% ends up being (I do not have a mind for math) Keep in mind its likely that as soon as you think you've got the magic % he will change it up on you.

It might end up that he is a kitty that overall does better with a diet at the higher end of the LC range
Under the best of circumstances going down the dosing ladder is a much more emotional ride than going up - I speak from experience. It's also nearly impossible to do gracefully - there are bumps (like the dreaded fur-shot) and pitfalls along the way.
Ultimately its a dance that the kitty is leading and we humans sometimes have trouble following - we aren't as agile.
You are doing a great job.
Hang in there and hang in here
