Nether caves not filling to sea level

Nether cave lava seems to be hardcoded at 32, the default sea level, and cannot be changed in any way.

 

If the depth of the world is decreased, it is still always 32 blocks above the bottom.

 

Edit: Added a reference pic. The one to the right is the sea level, and you can see on the left it stays hardcoded at 32 above ymin