Colour-coded sketch of the molecular clouds and Fe-Kα line flux variability studied in this work. The circles and ellipses represent the regions selected for the timing and spectral studies (see also the right panel of Fig. 2). The colours are blue (increase of the 6.4-keV line flux), red (constant) and yellow (decrease). A Galactic coordinate grid, and the positions of Sgr A* (green star) and the Arches cluster (cyan stars) are also indicated.