Top row: heavy element masses of the planets simulated in the discs of WASP-84 (left) and CoRoT-9 (right) as a function of the initial position of the planetary embryo. The observed heavy element mass is shown as a dashed red line, with its uncertainty indicated by a red shaded region. Bottom row: predicted atmospheric C/O number ratios of the same planets as a function of initial position. The dashed red line shows the best-fit formation location based on the heavy element mass, and the grey region indicates the constrained range of possible formation locations. H₂O and C evaporation fronts are shown as dashed black lines in all panels. All simulations use α = 1 × 10⁻⁴.