Given the fact that collector area is very cheap, I should have mounted the panels vertically directly on the wall. It would have saved me a lot of work with the mounting angles and a lot of expensive stainless steel screws, which in turn would have allowed me to add one more panel (the lower row maybe with 3 vertical ones?) without higher costs.
This would have looked a bit nicer, and the efficiency in november/december/january would have been better due to the larger area. In addition, the subventions given by the German state are higher for panels that are mounted vertically on the wall... And the panels would have had a better isolation from the back, and they themselves would have isolated the wall a bit more.
Disadvantage of that idea: in summer, the upper collectors would not have shaded the lower ones, but as the efficient area is much smaller... well who knows. Depends on the relation of diffuse to direct sunlight, which I do not know, and which is not constant. As a result I can not calculate the effects correctly.