Not sure about the validity since custom dimensions are still currently experimental.

In the provided datapack's added dimension, despite the buildable range being locked between y=-2031 and y=-2016, the (bottom half of the) sky will always turn completely black if the player is below y=-1.62000, despite this obviously being extremely far out of the reasonably acheivable y range.

This could be fixed by making this "blackening" point always be at or around the min_y point in the dimension or halfway up from it, or, even better, made configurable itself.

There also exists a second darkening effect below min_y, which could also be made configurable independent of min_y in the process if independent configurability of the other darkening effect is implemented.