Allan, the sun rises in the East , tracks through South to set in the West.
The angle the panel is set at is not critical as long as it is facing the sun, approximately.
The difference between it laying flat on the van roof, and being angled can make a difference of about 1 volt on a good day, and if you want to make the most out of the sun, then you have to keep altering it both axially and angle as the sun rotates and rises and sets