The washer jets could be set so that they work best when on the move. It is
a trade off - set the jet to clean the screen when at a standstill, and they
wash your rear screen when on the move, or set the jets so that they
wash the screen when on the move and they are then too low when standing.
I have two pairs of jets, so, in each pair, I have set one jet higher then the
other to achieve a working compromise.