And for the condensation process, the direction of the surface does not matter.
It can matter. The condensation process depends on the temperature. And in this case the temperature of the object depends at least in part on what it "sees".
On a clear evening, the objects around the vehicle, the ground, any trees, objects, buildings, still have quite a bit of thermal energy from the day. Overnight, these objects will radiate some of that energy away as heat.
The vertical surfaces of the car are oriented in a way to receive that heat. The roof of the car is not well-oriented to receive as much. On an evening with less moisture in the air, the radiation temperature of the sky can fall quite low. This allows the surfaces that "see" mostly sky to drop to a lower temperature, below that of the water vapor in the air.
If the car were parked under a carport or under a tree, this would block the ability to radiate to the sky and (on a night where condensation could otherwise occur) there would be much less condensation than the same car parked in the open.