We have no clue what is causing the need for higher doses. It is all just guesses as Eddie isn't talking. But bad teeth and IAA have meant higher doses with previous cats. It is not something to be ruled out. I know you can't do anything about it right now, other than possibly keep up with pulse dosing of ABs. Acro growth is also a possibility, but we don't know which it is without more information. And it doesn't really matter, because the result would be the same - increase the dose when needed.
There are many signs of acro, and it varies by cat. Is his weight increasing? Is his snoring new or the same? Any separation between his teeth or is that changing. Any signs of arthritis or soft tissue growth? The not walking much could be arthritis - have you talked to the vet about that possibility? Once Neko got some relief from arthritis she became more interactive and playful. The vet could feel her bony growth, and even could I.

The heart is not the only organ that grows. A year ago he was down to 10 units. Are there any physical changes since then? Significant changes in blood work since then?
An interesting exercise a couple of us with acros did was side by side photos of before and after. See the side by side of punkin in post 9 of
this post. I would show you Neko's, but people guess wrong which was before and which was after.

Meaning, she didn't have those type of changes. Her worse signs was the arthritis.