How to reproduce:
1. Open the user's attached "PSX_shader_port.zip" project
2. Open the "SampleScene" Scene
3. Open the Fog settings (Window -> Rendering -> Lighting -> Environment)
4. Set the Start property in the Fog settings to 10
5. Set the End property in the Fog settings to 12
6. Observe the Fog in the Game view

Expected result: Fog starts from 10 to 12
Actual result: Fog starts from 0 to 12

Reproducible with: 10.2.2 (2020.2.2f1), 11.0.0 (2021.1.0b4, 2021.2.0a3)
Could not test with: 7.5.2 (2019.4.19f1) - Due to errors in the Shader Graph when downgrading

Note:
- The issue is not reproducible with Exponential, Exponential Squared Fog Modes