Replying myself (no comment
? ) about Silent][Moebius 's thought : the rear of the car is too long.
You'll find attached a quick comparison between the blueprint I'm using and a refpic. Size is not perfectly set but the problem with the rear is clear.
Bonus : a clay of my last fixes on the back. I did it before comparing blueprint vs refpic so it shows the problem too. Now working on sizing down the rear.