Ratio of the semi-major axes of a pair of planets using the disk configuration with Σ₀ = 100 g cm⁻², turbulence viscosity corresponding to α = 0.01, and including stellar irradiation. The planets are initiated according to the setup in Model 2. The outer planet transits the 2:1 MMR with the inner planet and becomes trapped in the 3:2 MMR, as in the model that does not account for irradiation (see Sect. 4).