Ratio of Roche-lobe size to the orbital semi-major axis as a function of the planet-to-star mass ratio. The size of the Roche lobe can be calculated using the distance of the planet centre to the L1 point (dashed line), to the L1’ point (dotted line), or by calculating the projected size of the Roche lobe occulting the stellar disc during a transit observation. The latter is about 2/3 of the size calculated by considering the L1 or L1’ points. The measurements for WASP-79 b in the NUV white light curve and at 2400 Å are plotted in red and blue, respectively.