How to control planar reflection intensity!

I added a planar reflection.
Iam wondering how to lower the reflection intensity of the floor material.

A roughness value of 0.3 as shown in the image creates reflections which are TOO strong.
Any roughness value above 0.3 as shown in the image below creates NO reflections at all.

It also seems that there is almost no difference between a roughness value of 0.05 and 0.3.
the reflections seem to be identical.

Any suggestions would be really appreciated. :blush: