Ratio of modelled photon flux to observed photon flux across various line formation temperatures (T_max). The top panel compares results with Brickhouse et al. (2010) and the bottom panel with Raassen (2009). Ratios are computed for individual emission lines and averaged in temperature bins of 0.1 dex. Error bars indicate 1-sigma observational uncertainties, and dotted lines represent the estimated range of the model uncertainty.