He I transmission signal strength for the planets with detections (blue circles with error bars in black) and non-detections (red down-pointing triangles in grey) as a function of the stellar F_XUV (λ = 5– 504 Å) at the planet distance. We show the equivalent height of the He I atmosphere, ${\delta }_{Rp}$, normalised by the atmospheric scale height, H_eq. Data from Table M.1 and references therein.