Atmospheric pollution and haze affected that dramatically
In fact a slight haze on a sunny day is the best light you can get. We get several amps more under those conditions.
Cooling was mentioned before as well, panels de-rate a lot when they get hot. That said I've never seen anyone do any active cooling, possibly the energy required to do that is more than the gains. Running water over the panels would be good but most people can't spare the water.
I would fix the angle but if it's easy allow for manual adjustment every month or two.
Rob