Notes. Each row of the table considers different effects. In addition to a full simulation of detection efficiency in the presence of instrumental background, foreground and point sources (tagged as “Sensitivity only”), we simulate the effect of source confusion (tagged as “Confusion”), effect of XMM PSF on increased detection due to more flux seen in group outskirts (“Confusion+PSF”), and 30% change in the normalisation of L_X − M scaling relation with (“Confusion+Scaling”) and without (“Scaling”) the effect of confusion.