Contour plots between kT_e and τ for the slab (left panel), spherical (right panel) and compact spherical coronae (bottom panel) are shown, for the 2013 and 2014 best fits. For the 2013 data set yellow, orange and red contours indicate 99%, 90% and 68% confidence levels. For the 2014 data set cyan, light blue and dark blue contours indicate 99%, 90% and 68% confidence levels, respectively. We show, for the sake of visual comparison, the 99% c.l. contours adopting extended spherical coronae for the 2013 and 2014 observations in gray (bottom panel).