Total FoM_TOT (top) and dark energy FoM_DETF (bottom) figures of merit as a function of median redshift of a stage-IV spectroscopic survey using a tomographic analysis (red triangles) and an SFB analysis (blue dots). The cyan line shows the figures of merit for the tomographic analysis when the number of bins is not adapted to the depth of the survey and kept at 30 bins. For the red-dashed lines, the number of bins has been adapted to each median redshift. In all cases, a grid of 5 × 5 nuisance parameters in scale and redshift is used to parametrise the galaxy bias.