H/He envelope mass M_XY as a function of heavy element mass M_Z for synthetic planets with semi-major axes 0.11 ≤ a/AU ≤ 5. The populations in the top panels and the bottom left panel only differ by the value of f_opa as indicated in the plots. The populations were calculated assuming full non-isothermal type I migration rates. The population in the bottom right was calculated with f_opa = 0.003, but without orbital migration and assuming Ṁ_Z,run = 0. The lines show simple analytical estimates and scalings (see text).