As well as is done in some offline engines like Thea Render you can add a coating layer over your material and it will add a second reflection layer.
Ie imagine a very rough surface like 0.7 roughness with a shinny coating like 0.1 roughtness, mixing that in ue4 you’ll get a 0.4 roughness not the effect of both combined
Reference from Thea for SketchUp