AWR2243: The cascade of AWR2243

Hi all

I see  TI has a cascade board of four chips of AWR2243 (tidm464)

When i check the design files of this demo board , i find that it uses the material of R04450F for the Dielectric 2.

The RO4450F only has 4 mil thickness and the Dielectric Constant is 3.52 in Rogers datasheet

But in TI's demo board files that it is not the same as the datasheet of RO4450F.

So i want to know why does they are not the same? 

Thanks