I had a long conversation on discord on how the PBR and Ubershader Fresnel seems to be incorrect. The main problem is that the PBR shader with a Base color and Metalness connected does not produce any fresnel on the surface. Both the dielectric and conductor materials seem to have no fresnel. Example Below.
The same thing will happen if you setup a Uber Shader with the Reflection Mode set to Metalness.
To illustrated how the PBR fresnel is suppose to look, I was able to setup two Uber Shader (one set to IOR 1.5, and the other Set to Metalness), and mask the metal with a Blend Material node. It should look like this.
If you look at the seat/gas tank area, you can clearly see fresnel reflection, but it is missing if you use the PBR or Uber Shader set to metalness.
As a comparison, I've also attached a render from arnold PBR shader to show its fresnel.
The examples above are from 3DS Max, but I've seen the same behavior in Blender 2.8 with the Principled material.
f you have any questions, please let me know.