Mass-radius relationships taken from Zeng et al. (2019), shown with orange, light blue, and dark blue lines, are (a) 100% made of rock with an Earth-like composition (i.e., 32.5% iron and 67.5% MgSiO3) (b) 50% made of an Earth-like rocky core and 50 or (c) 100% pure H2O. The purple line shows the M-R relationship for a constant density of 3.2 g cm⁻³, the default used in this work. The increasing ρ model is a fit to the rocky core composition. The decreasing ρ is the minimum decrease in core density that affects the gas accretion rate. Since the gas accretion rate is only altered when the core’s density is significantly lower than interior models predict, we conclude that our assumption of a constant core density does not significantly influence the results.