For what I know you have Fresnel everywhere and as you have reflections in metals you have a Fresnel term http://sirkan.iit.bme.hu/~szirmay/fresnel.pdf
Thanks! But that would be that “micro” effect of Fresnel which gives the “metallic” colour shift to reflected light, right? The shift we are used to faking through explicitly setting spec/reflection colours. Not the general “macro” dielectric Fresnel thing that makes reflection at glancing angles stronger overall, without colour shifting.
And the Fresnel term in the Uber family (and in generally popular shading models like Cook-Torrance as well, I think) only works for the latter, “macro” effect.
As for “how”... now that’s a question I´d like to ask Omnifreaker actually, “how come you did not include at least an option to properly base Fresnel on IOR?!” LOL It’s a giant pain to try and approximate real IOR-based Fresnel behaviour with those controls.
Speaking of “physically plausible” shading, have you tried it? I haven’t yet… I’m still basically teaching myself to write “oldschool” RSL, I’m not sure it’s worth skipping the “basics” in favour of the shiniest toys…