4A. See details . They mention that this shows up for Al and Si anodes as well. The focal plane FPC data were normalized to one of the BND-H FPCs. Horizontal lines are model predictions based on TMA area and rectangular grating approximations.
Horizontal lines are again the rectangular predictions for comparison.
There is mounting annecdotal evidence that the focal plane FPC may have lower low-energy efficiency than predicted. But when the FPC was put at zero-order with a 36 mm aperture the count rate was very low. Dan, I hope MY data gets treated with appropriate respect. Anyway, you might want to look into this or maybe you already know the explanation. Dick Elder did experiments to determine the NE80 values and notes the importance of having the beam-splitting cube aligned in all three axes.