Since the defeat of the Fiends, the major powers had been quick to build several layer arrays. There were no ascension pools like in the lower realms.
The Celestial Fields were all Immortal, it was simply the density of Laws and elemental Qi that changed. It was all still Immortal.
Tribulations allowed for a natural progression if they were overcome, but artisans had long learned how to safely create the effect of bridging the layers. So long as the rules of Heaven and Earth were not violated, the Sliver to the Radiant Tiers could move up to any layer they wished or down to the layers that could withstand them.
Now that the barriers the Fiends had put in place were long gone, travel between layers had become more common.
Still, the 4th layer was a special place as it was one of the few layers to largely survive intact without any drastic changes needed. Only the 2nd layer could compare in that regard as the other 2 were decimated by the Fiend's plans.
