The nether fog behaves rarely when going deeper than y=0

The bug

The nether fog behaves rarely when you're located deeper than y=0. It should display a gradient instead of going from 'full-vision' to 'no-vision' (see video attached).

How to reproduce

1. Go into spectator or creative Mode

2. Run '/execute in minecraft:the_nether run tp @p 0 0 0'

3. If you look above, you can only see a circle of bedrock and there isn't any gradient or anything like that