Semi-major axis versus radius distribution of synthetic and observed planets. To put TOI-2406 b into perspective, the population of predicted core-accretion planets from the 0.1 M_⊙ case in Burn et al. (2021) is shown. The metallicity of the host stars is colour-coded and used in the theoretical calculations as a proxy for the initial planetesimal-to-gas-mass ratio. The metallicity and planetary radii for TRAPPIST-1 are taken from Delrez et al. (2018b) and Agol et al. (2021), respectively; those for LHS 1140 from Ment et al. (2019) and Lillo-Box et al. (2020); and those for GJ 1214 from Anglada-Escudé et al. (2013). Those systems are in better agreement with the theoretical calculations than TOI-2406 b.