Semi-major axis evolutions of planets forming in the disc of WASP-84 (top) and CoRoT-9 (bottom) for discs of different viscosities: α = 1 × 10⁻⁴ (left), α = 5 × 10⁻⁴ (middle), and α = 1 × 10⁻³ (right). Red circles indicate the time and position at which the planet reached its observed mass for each simulation. All plotted evolutions are for simulations that matched the observed heavy element masses of WASP-84b and CoRoT-9b. In the disc of WASP-84, for α = 1 × 10⁻³, the observed heavy element mass could not be matched by simulations for any initial position.