I am writing an urban fantasy story set in the late 90s/early 00s revolving around the societies of magical immortal beings that secretly live amongst the human race. Despite their magical genetics being completely passed down even to children they have with humans, these immortals have consistently remained a 1-in-1000 minority amongst humanity, rather than displacing it, due to a quirk of how my world operates that creates consequences for immortals when they get too numerous in an area. However, I recently realized that this quirk needed major modifications, and now that I have made them, I've realized this causes problems for some of the settings I have already created and which now must be revised.
The New System
Unbeknownst to the human race, there is a secret 25th hour, the Witching Hour, which occurs once a day when it's approximately 3 AM in Ireland. During this hour, all time stops for anything and anyone non-magical, before returning to normal at the end of the hour. Under normal circumstances, that's all that happens. However, the Witching Hour is considerably complicated if too many immortals are concentrated in one area.
As far as immortals currently understand it, immortals seem to produce a sort of "magical exhaust" as a byproduct of their magical abilities and existence. This is measured in fels, where one fel is defined as the amount of magical exhaust produced by one immortal in one day. The planet absorbs a minimal amount of this exhaust (one fel per day for every 300 square miles), but humans seem to absorb a great deal more (1 fel per day for every 1000 humans). As long as the immortal population in a given area remains at or below 1 immortal for every 1000 humans, the area's fel count remains at zero and the Witching Hour is normal. But if they go above that, the fel count in the area begins to rise, and this has massive consequences on the Witching Hour.
For reasons unknown, when the Witching Hour arrives for an area with too high of a fel count, for the duration of that hour reality begins to warp in dangerous and unexpected ways, frequently described "as if the planet itself is having a nightmare". Anything with a fel count above 50 is considered extremely dangerous, and there isn't a single known, confirmed case of an immortal surviving the Witching Hour in a place with a fel count of 100 or greater. In addition, once the fel count in an area exceeds 120 or so, it caps there and any additional fels begin to spread out into adjacent areas.
Long story short, the previous system, among other things, had the dangers of high fel counts be a monthly occurrence rather than nightly, be far more predictable and realistic to mount a stable defense against, and return the fel counts to 0 when they were over. Under that system, I had developed the PRISM Consortium, the center of magical commerce, business and trade (as well as its most shameless wellspring of mercenaries, prostitution and narcotic potions), where the secret immortal population was run by an extremely libertarian organization whose attitude towards the monthly dangers was to rely on privately-owned safehouses that sheltered people from the dangers of the Witching Hour for a price, let the fel counts rise as high as its people could afford to survive in, and let the weak, foolish and/or unproductive be the first to be culled when the population gets high enough that people start dying.
That attitude might have "worked" under the previous system, but it's completely unsustainable now. Now, even if you let nature run its course and let a population reach "equilibrium", the fel count will stay at that dangerous level, and now the only reliable protection that money can buy from a place with a high fel count is "not living in one". The PRISM Consortium needs a reliable strategy for keeping its fel production at a net neutral or negative, or it will become unlivable in a matter of months to days.
The problem is that I still want this to be a society that's big on individual liberty and free markets and small on social safety nets and public services, to contrast with another society in my story which lies at the opposite extreme. But it seems like every societal solution I can think of to keeping fel counts low involves some form of telling people where they can and can't live and travel, which not only feels entirely antithetical to the society I've envisioned, but also highly problematic for a place that prides itself on being a megahub of trade.
To be clear: the solution doesn't have to be pretty, as the previously-planned "solution" illustrates. This isn't a dystopian setting, but its intended to be imperfect and flawed and have serious problems with it, just like every other society in my setting to varying degrees. The solution just has to work enough to prevent societal collapse.
How could the PRISM Consortium keep its fel counts from getting out of control without micromanaging where its people and visitors can and can't go?