In terms of aiming the sub correctly to ensure it is firing in a way that the sound is not inhibited - the position changes according to the car
Also the size of enclosure, sub, etc is going to affect the prime aiming position
Good aiming is very difficult in a hatchback like the Clio. I ,yself find that my sub is happy one side of the car, facing the opposite car. aiming at the boot makes it too muffled. Its probably best to aim it slanted so its firing at the rear screen