Measured He I absorption signal as a function of stellar XUV flux and planetary gravity. Top: Size of the measured He I absorption signal, normalised to the atmospheric scale height computed considering the planetary parameters listed in Table 3 and a mean molecular weight of a pure hydrogen atmosphere, as a function of the incident stellar XUVflux (in logarithmic scale). Upper limits are marked by downward arrows. The symbol colour indicates the spectral type of the host as given by the legend. Bottom: Same as the upper panel, but as a function of planetary surface gravity.