The DFF-Mono pattern is interesting because of how if you reduce the high-cut you can see the bands disappearing step-wise in decreasing density... I assume this occurs as the Nyquist frequency is passed for those pixels?
No, the Nyquist frequency isn’t the relevant parameter here. What is happening here is that you have a low-pass filter with a very steep cutoff (or high-pass, depending on what you are sweeping). As you sweep the cutoff, because the filter is so steep, the band suddenly disappears when the content moves from one side of the cutoff to the other.