if your panel in an “arc” I am still surprised that you are so flat in your output . it would appear to me that you have one inverter and they are pushing both sets of panels through it and the inverter peaking out at 3800. not knowing your “arc” position or angle but if it 6kw I would think it should be peaking at around 4500 maybe even 5000 on a clear day . I find having 1 inverter for doing an arc configuration is like a battery it only preforms as well as the weakest cell allows it - if you want to see if that your problem disconnect the west cell mark down the output of the east. then disconnect the east cell and mark down the out put of the west . add the two together and if it over 3800 then then you know clipping is happening