So depending on your latitude you’ll want 30 to 45 degrees vertical, and about 17 degrees SW facing if you can achieve that. Best case you have perpendicular angle of incident with the photons from every angle.
Discussion
Yeah. The next two panels I install will be on tilt mounts, and I'm going to split the pairs differently. That should yield way better results.
Some other things to remember, panels at different voltages, ie. shade and sun will feed power from one into the other if you don’t separate them with diodes. Some panels have them built in, but most don’t. I found 15A MC4 diodes on EBay. Also, cooler panels make more power in the same sun. Some people go for a SE facing array because the local atmosphere helps keep the panels cool in the morning sun. Even a partially shaded panel can affect the overall production negatively.
My panels have diodes and are very efficient, putting it full voltage in rather adverse conditions. As long as I split the panels into a morning and afternoon array, I think the output will be acceptable in the winter.