Left panel: source plane coverage of each cluster at z = 4, as a function of the strong lensing magnification of the most magnified image. The black square shows a 1 arcmin² for scale. Right panel: effective volume surveyed at 2.9 <  z <  6.7 with MUSE for Lyman-α emitters, as a function of the magnification of the brightest image. Presented are individual volumes behind each cluster and the total over all fields.