Wish: Ground plane reflection respect POLISH and "plastic" material

Hi, I see that GroundPlane require the material to be sat to Custom to support reflection.
And that it ignores Reflection Polish.

Could it respect Polish? Or is this just a geometric trickery where the geometry is drawn mirrored around the groundplane?

If possible I would also like Ground Plane reflection to work on other material types than Custom. (like plastic and metal)