I have zero shading on my aft roof, where the panels are mounted. However, they are horizontally oriented, so I'd expected to lose 25-30% efficiency. The reality is looking like 33%, with peak performance logged at 41amps. The really cool thing is that, once I'd stopped checking the numbers every five minutes, the thing just quietly works away in the background. I'm sure I'll just start taking it for granted shortly :-). Oh, and it does work when it's overcast...20amps is pretty well the minimum I've seen.
Of course, as the bank SOC gets above 85% or so, the controller steps back, and I don't see any amps....