When the almost vertical glass on my GTI with rear compared to my wife's M.3, it's not contest, the GTI is always a dirt magnet to vs the 3 looking like it never have encountered dirt.Rear wipers are actually more necessary (possibly required?) on close to vertical rear glass, because it's more prone to accumulating road grime and the airflow detaches before the glass so can't clear it. On the Model Y (or a sedan) you have less problem with rear glass debris because the airflow remains attached over the glass.