Schematic of the method used to measure the ¹²CO surface z/r values. Each surface traced by the grey line is the output of a T Tauri model, in order of increasing height and radial extent they have disk masses of 10⁻⁴, 10⁻³, 10⁻², and 10⁻¹ M_⊙. The shaded red curve shows the best-fit parametric model fitted to the molecular surface, from where r_taper is the taper radius. The measured z/r is obtained by fitting the surface region within 80% of r_taper, this distance is indicated by the vertical dashed line. The characteristic z/r is traced by the straight black line for each surface.