for some reason I now miss the opportunity to change the final level of reflections using a spinner or a BW map, sometimes it helps a lot in bringing the floor material to realism, now you have to create a composite map with two ior values :DDD
Can you explain what exact property you would like to change?
With the new physical material, you should be following the metalness/roughness workflow. You can map metalness, roughness, and IOR.
Of course I understand that I should use a metallic / roughness workflow, there is no problem with that) and of course there is a direct relationship between roughness and the strength of reflections, the same as it was in legacy corona mtl
And despite this, there are some materials in which, to achieve better results, sometimes it is necessary to tweak the final strength of the reflections with spinner or B&W map, and its not very convenient to do this by mixing two linear ior values
as an example, lets take a flooring material, let's assume I use a generator from Poliigon and at the output, in addition to roughness, I will also get a specular level (pic1) but unfortunately now I can't use it directly but only as a mask when mixing two IORs, in fact it is not a big problem, except that mixing different IORs give a slightly different result from simply reducing the strength of reflections. e.g. in legacy mtl i used speclvl in reflection color slot with about 5-15% of opacity