Measured stellar velocity dispersions of 22 MUSE spectroscopically confirmed cluster members as a function of their EuclidH_E magnitudes. Their colours encode the mean signal-to-noise ratio of galaxy spectra. The black solid line is the best-fit (maximum likelihood) of the scaling relation in Eq. (9). The light orange band corresponds to the best-fit mean scatter, Δσ_ap, around the best-fit relation. The red solid curve corresponds to the relation in Eq. (9) as obtained with the best-fit parameters of our reference model (see Sect. 3.1). The light red area is estimated from 300 random values of σ_ref extracted from the Bayesian MCMC realisations of the reference model of this work.