Fits to the standard deviation σ_Pθ of the photocentric motion predicted from 3D simulations, as listed in Table 3, against the pressure scale height H_p. The equation of the (red) solid line is log σ_Pθ = −6.110 + 1.110log (H_p) with χ² = 0.17: the fit considers only the box-in-a-star models (filled circles) of Svensson & Ludwig (2005). The (green) dashed line (with equation log σ_Pθ = −6.275 + 1.174log H_p + 0.039(log H_p)²) is a fit to all the models of Table 3 (i.e., box-in-a-star models and star-in-a-box, the latter being represented by a filled square). The (blue) dotted line is an arbitrary exponential law that connects the last two points with the following equation log σ_Pθ = −1.09−3.434exp(− 0.00149H_p).