Before 2.79 I used a dialectric node setup outlined by Andrew Price for PBR materials. This involved "reflectivity" maps among other maps, which I used, and many PBR texture maps include the reflectivity map. But I see no "reflectivity" value in the new Principled Shader. Where do I plug in this map? I know it's not roughness, because that's its own thing, and I know that the "specular" value probably isn't it, because I've heard multiple people say that that value isn't for when you're trying to do physically accurate shading; that it's not a PBR-related setting. I know there is some other PBR-related value I'm not using that affects reflections, because I plug in roughness and normal maps for very rough, dull materials, and they still look shiny.
Thanks for any help y'all can give!