Ratio of the difference between the temperature values obtained using XMM only in the background region (T_NORASS) and that obtained with our standard pipeline (T_RASS, joint fit with RASS in the background region) over T_RASS, in percent units, as a function of the SOU/BKG ratio in the spectral region. Filled points show the individual measurements (error bars not shown for clarity), while the open squares represent the weighted mean ratio and its error in different intervals of SOU/BKG. Blue points refer to measurements in clusters with R₅₀₀ > 9′, red are for the remaining objects. The cyan triangle shows the median value for the regions with SOU/BKG < 0.2 and clusters with R₅₀₀ > 9′, significantly different than the mean with the same criteria.