Test of the stability of the background model as a function of the detector region used to normalise the background. δP is the percentile variation of the observed blank-sky background with respect to the background model in the normalisation band (9.5−10.6 keV). Points correspond to the different analysis strips. The eight panels correspond to the eight different regions used to normalise the background (see panel title). Dashed lines indicate the accuracy of ±2%.