Effective temperature difference between observations and models as a function of different observational parameters. Left: ΔT vs [Fe/H]. Colours identify stars as in the APO-K2 catalogue (green = high α, blue = low α, red = transition). The black solid line represent a loess smoothing of the data. Open circles show the trend reported in Salaris et al. (2018), while open triangles show the trend by Tayar et al. (2017), shifted downward by 100 K. Right: Same as in the left panel but as a function of [α/Fe].