The problem with that is that will cause areas to drive up housing prices to expand the untaxed group to general more “upper middle class” to price out undesirables and draw in higher earners as a form of tax break. This already happens without the tax bracket scaling and would probably get 10x worse.
I don’t have a great alternative, but maybe a weighted CoL combined with 0% below median income in the district? Something like that, but that would probably cause low CoL areas to pay way more taxes. Maybe I am thinking of it wrong.