Near-infrared transmission spectra and best-fitting models of the five sub-Neptunes that occupy a similar part of parameter space in Figure 15. The spectrum of TOI-421 b and its accompanying best-fitting model are from B. Davenport et al. (2025), the spectrum and best-fitting model for GJ 1214 b are from E. Schlawin et al. (2024), and the spectrum and best-fitting model for K2-18 b are from N. Madhusudhan et al. (2023). Neither TOI-836 c (N. L. Wallack et al. 2024) nor HD 15337 c has detected features so we show the corresponding best nonphysical model consisting of a step function to account for the offsets between the two detectors for these planets. There are currently no NIRISS/SOSS observations of GJ 1214 b, HD 15337 c, or TOI-836 c.