Left: derived envelope mass fraction as a function of radius for the planets in our sample. The dotted black line marks the 50% f_env threshold. The gap in f_env for the different retrievals coincides with a gap in radius between 6.2 and 7 R_⊕. Right: distribution of f_env as a histogram for different age thresholds. Planets are distributed in subsamples of planets older than 3 Gyr within 1 σ, planets older than 1 Gyr within 1 σ, and all planets initially considered for the sample before the age cutoff. On top are kernel density estimator functions based on the subsample. The bimodal shape of the distribution is independent of the age threshold.