Evolution of the FoM as a function of the inverse of the standard deviation of the new observable, for the test cases considered in Sect. 5.2. In blue, the case where fiducial values of the spectroscopic biases are taken to be equal to the photometric biases (bottom plateau at FoM=1234 and top plateau at FoM=1567). In red, the case with different fiducial values of the spectroscopic biases and photometric biases following the baseline of EP:VII (bottom plateau at FoM=1250 and top plateau at FoM=1606). The FoM includes the information from GC_sp, 3×2 pt, and the new observable.