You also have to take into account that early in the morning and later in the afternoon, panels in series will still have enough voltage to keep your solar controller running. It's almost always better to run panels in seriesRenogy's website states their 100W panels have bypass diodes.
It would be really interesting to see real numbers on actual voltages and amperages (and resulting wattages) on 2 panels in series vs 2 panels in parallel with various shading patterns applied to the two pairs of panels. That might help narrow down which shading patterns would indicate using serial panels versus which patterns are better handled by parallel panels.