Decimal logarithm of the reduced chi-square for the effective radius between our 3D model and the full forward model from TauREx over a range of temperature between 200 and 2600 K and of R_p∕H between 40 and 260. As a comparison, all planets described in Fig. 4 have R_p∕H > 100. The black line shows where the reduced χ² equals unity, i.e. where model differences become insignificant compared to the noise. We assumed an error calculated with a sun-like star at 100 lyr, 1 h of integration and JWST instruments. The same work has been done for four vertical resolutions: 50, 100, 200 and 500 layers.