leanFIRE ACA income estimation Catch-22

Assume a retired person above 138% FPL but well below 400% FPL, whose only income is whatever they need to generate, in my case) to meet their expenses.

They spend [X] per year, before healthcare costs. They provide the ACA that number as their income estimate.

Except the original income estimate is insufficient, because they need to add healthcare costs. And more spending means generating more income.

Which means the costs will go up, which means they spend more, which means they need more income, which means healthcare costs go up, which means they spend more, which means they need more income, which means [...etc]

Then they get unlucky and need expensive treatment and hit their $9000 OOP max, and thus need to spend more, and thus need more income, and thus underestimated their income [...etc]

Like I guess the answer is just "try to leave an appropriate enough buffer and true-up at tax time", but is there a more elegant way to handle this?