Help with symmetry
 

I'm modelling a car mockup in a wind tunnel, and I'm defining a symmetry plane along the longitudinal axis of both. I'm interested in the Cd an Cl of the car buy I've a doubt: In the turbulence specification method (in hidraulic diameter) and in the area of reference values, I've to introduce the total front surface of the car mockup or only the half value of this surface due to the symmetry used? Thanks a lot.