KA4FRH 2^nd Filter Flatness Measurements

These plots were taken after installing the resistor that belongs with the 2nd filter flattening modification. However, the parts included in the kit that I got included a 120pf capacitor rather than a 100pf capacitor and no resistor. Furthermore, the resistor was not mentioned in the modification instructions. These plots are with that capacitor and clearly show adequate flatness in SSB mode but only for the unused mode on the bands tested, i.e. USB okay on 40m and LSB on 15m rather than the other way around.

He question is why is the filter flatness dependent upon which SSB mode is in use?