Sheen in Unity doesn't match web result

### Describe the bug 💬

Sheen effect in Unity does not match sheen in Needle Engine / three.js based viewer

unity:


web:


gltf.report


PBR graph:


### Steps to reproduce 🔢

1. Download https://sketchfab.com/3d-models/retrowave-sportcar-low-poly-model-f239927bfe2643c1a3e6eb235f58b526
2. Extract body color material
3. Enable sheen
4. Set sheen color to blue and sheen roughness to 1
5. light sheen color in unity
6. export to glTF and open in https://viewer.needle.tools
7. Note sheen looks much stronger than in Unity

### Files to reproduce the issue ♻

https://sketchfab.com/3d-models/retrowave-sportcar-low-poly-model-f239927bfe2643c1a3e6eb235f58b526

### Editor Version 🎲

2021.3

### Render Pipeline and version

12.1.13

### UnityGLTF Version

2.14.1

### Operating System 👩‍💻

Windows

### When does this problem happen?

- [ ] Editor Import
- [ ] Runtime Import
- [x] Editor Export
- [ ] Runtime Export

### Additional Info 📜

_No response_

### Validations 🩹

- [x] I have [searched existing issues](https://github.com/KhronosGroup/UnityGLTF/issues): no issue already exist that reports the same problem.
- [x] I follow the [Code of Conduct](https://www.khronos.org/about/code-of-conduct)
- [x] I provided a [minimal reproducible example](https://stackoverflow.com/help/minimal-reproducible-example), including files when necessary.

Reproduce the export using the linked Sketchfab retrowave car, Unity 2021.3, and the stated render pipeline and UnityGLTF versions. Compare the Unity sheen with the exported glTF in the Needle viewer and gltf.report; done means the exported sheen matches the Unity result.

Written by the indexing model from the issue text.