How can energy seeping into reality be prevented from spreading?

Question

Our reality is separated from the realm of chaos by a thin barrier that prevents either realm's inhabitants from interacting. The exception is during an event which occurs every 1000 years. In this scenario where the sun, earth, and moon align, it causes a solar eclipse, which opens a path from the chaos realm into our world. Think of a balloon which has a hole, allowing outside air to come in and deflate it. The barrier is bypassed, allowing demons to flood into our reality. Fortunately, this event is temporary, and demons lose power closer to the end of the eclipse. When the event is over, the energy sustaining the demons dissipates, and the spirits fade back into their realm.

After the devastation, the world does what it can to go back to normal. However, some of the energy from the chaos realm coalesces in certain areas. This is the generation of certain "haunted" locations, such as houses, caves, etc. The evil spirits are sustained by the power of the remaining energy, harming or killing anyone who trespasses.

However, there is a flaw in this logic. After a rip in a balloon is repaired, it isn't fixed completely. Even a small tear will allow air to penetrate, which will eventually cause it to deflate. At best, you have only bought time. These trapped energies in various locations should be spreading to the rest of reality. Instead, they are trapped in these locations, frustrating the spirits within as it prevents them from leaving. Why would this be the case?

Answer 1

The energies are puddles.

The analogy is not air, but water. The event is like a rain. These malign energies accumulate in certain places like water - low spots, as it were. Some of these spots are left over from 1000 years ago and reaccumulate energy from the millennium event. Other low spots might have occurred in our world for unrelated reasons and are energized by the event.

The demons, like water creatures, are confined to the water. In our plane the nature of these malign energies is to dry up over time, like puddles after a rain.

Answer 2

Survival:

Your entities are frustrated by their inability to leave, but they're doing it to themselves. They are the ones concentrating the energy they need to survive. If the energy can spread, it rapidly becomes too diluted and they can no longer survive or they go dormant. They can't take energy with them, only stop it from dispersing. Therefore the places with energy are the places with spirits, and the places with spirits are the places with energy. Maybe places with lots of spirits can hold enough energy to allow spirits to slip out on a very limited basis, but only if it's germaine to the story - the other spirits hold the energy in place so the traveling spirit has a place to come back to. Maybe people can carry the energy with them, so spirits can use humans to piggy-back on while moving about. That's up to you.