I don't know enough about aerodynamics but find it hard to comprehend how spray can come back so far over the back of the body from the wheels under such a large rear wing but I suppose it is the answer
Unless it is wet spinning off the side of the tyre or flicked up from the front and then getting caught in some airflow around the cockpit
2008 XXVII Platform, Bugatti Blue Roadster 4 Seater