Change the coordinate system so that sea level is the reference point.

Now, the ocean surface (62) and the surface of the lava in the Nether (31) will serve as the zero coordinate.

Everything above this will have a positive coordinate, and everything below will have a negative coordinate.

Just like in real life, world height will be measured relative to sea level.

To me, this would make the world easier to understand.

It also allows for a height-based relationship between the Nether and the Overworld: if you build a portal at or below sea level, the corresponding portal in the Nether will be at lava level; if you build it above sea level—or even on a mountain—it will be positioned above the lava.