There was something about PID too and they were saying that with a panel tilted a bit, you can get a puddle at the low end dammed by the frame being a tad higher than the cells, which then sort of leaks into the works. Not too clear on that risk.
IMO go flat and just keep them clean.
Direct sun normal to panel gives the most amps and amps go down more the angle is off direct. Additional 10 degrees not linear so makes it more in the shoulder hours, when the flat panel is already at a disadvantage for angle.
full_mosey posted about this if I can find it.
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/25542183/gotomsg/25562549.cfm#25562549
