True (circles) and false (arrows) positive rates of the MCMC/BIC classification method as a function of the velocity separations derived from the simulations for increasing S/Ns (from left to right in the panels) and different spectral dispersions (shown as different colours). One-dimensional slices (in Δv space) of the 3D GP interpolation of S/N, dispersion, and velocity separation are presented as the coloured lines and associated 68% confidence interval regions.