Comparison of semi-major axes obtained through simulation with different theoretical models. Top: orbital evolution of our FM, along with two semi-theoretical models from Paardekooper et al. (2010, without a gap opening) and Kanagawa et al. (2018, with a gap opening), alongside two additional simulations using the same disc properties as the FM but focussing on individual planets. Solid lines represent the semi-major axis of the inner planet, while dashed lines represent the outer planet. Bottom: evolution of the quantity (a_p – a_sim)/a_p, where a_p represents the semi-major axis according to pure type-I migration and a_sim denotes the semi-major axis of both the inner and outer planets in our FM, as well as the single small and big planets in our single-planet simulations. The period of resonance is indicated between the dark and light grey time intervals.