Comparison between the different ways of reducing the data of HD 159222 with the PSFF fringe flat. The curves are (from bottom to top) the photon conversion efficiency of the MIRI MRS detectors; the reduction without spectrophotometric calibration (PHOTOM) applied; the results after applying the commissioning PHOTOM; and the new dedicated PHOTOM. Band 4C is omitted due to low signal. The red box indicates the spectral leak.