You could surely extend the "tunnel" out in front of the car, provided the cantilever doesn't make it bounce too much and it's out of the high pressure area.
However, while decreasing the model's scale the speed of the air has to increase exponentially to get useful results. If I recall correctly it's something like this.
1/1- 20mph
1/2- 40mph
1/4- 80mph
1/8- 160mph
etc.
Essentially unless you have a quarter scale or larger model you won't get useful results. Phil can correct me the numbers are off
