Question about Goal Zero Boulder 100

Under a cloudless August sunny sky, the connected Yeti 500X shows me a maximum input of 60 watts. What does the 100 watts mentioned refer to? And I also find the following very disturbing: The surface of the solar panel consists of 36 individual elements. As soon as I cover just one of these elements completely with a sheet of paper, the input power displayed for the Yet 500X drops to 0 - 5 watts. Is this normal? (Because I have the solar panel on the balcony, I now always have to make sure that the whole panel is completely in the sun and that no object casts even a small shadow on it).