S/N of the brightest [O II] spaxel against the apparent size-to-PSF ratio. The hatched grey region marks the parameter space excluded by our selection. Red symbols mark 6 galaxies chosen to showcase the range of apparent sizes and S/N in Fig. 6. Open symbols mark galaxies that are either dispersion-dominated (v_1.8/σ₀ ≤ 1) or have poorly constrained velocities (Δv_1.8/v_1.8 ≥ 30%), where Δv_1.8 is the posterior standard deviation. The background hexagonal bins illustrate the fraction of rotation-dominated (v_1.8/σ₀ > 1) mock galaxies with a robust velocity recovery ($|v_{1.8}^{\mathrm{fit}}-v_{1.8}^{\mathrm{true}}|/v_{1.8}^{\mathrm{true}}<30\%$). Bins with less than 20 mocks are not shown.