Hi @bit_man,
Yes, to a 1 to 1 scale preferably to reduce any complications.
If the car length is represented by distance L, the length in front and side of the car should be 5L, the rear 10L and the top 3L. That is very general however. Only specific literature can dictate what specific boundary lengths you need.
Do post your project link if you need further help.
Cheers.
Regards,
Barry