Ratio between the composite disk+bulge 3D half-mass radius and the 2D projected disk effective radius (r_{1/2, 3D, baryons}/R_e, disk; left) and the difference between the dark matter fraction estimators at these radii (; right), as a function of B/T, for a range of disk intrinsic axis ratios (colored lines, from q_0, disk = 0.05 to 2) and ratio between the bulge and disk R_e (solid, dashed, and dotted lines, for R_e, bulge/R_e, disk = 0.2, 0.5, 1, respectively). The adopted galaxy values are the same as in Fig. 6, except R_e, disk is now determined by R_e, bulge/R_e, disk. With a non-zero bulge contribution, r_{1/2, 3D, baryons}/R_e, disk deviates from the single-component ratio (Fig. 2), decreasing with increasing B/T for R_e, disk = 2, 5 kpc for all q_0, disk (increasing, however, with B/T when q₀ < 1, R_e, disk = R_e, bulge = 1 kpc). For large B/T and R_e, disk = 5 kpc, the composite r_{1/2, 3D, baryons} is less than 50% of R_e, disk. If the dark matter fractions are measured at different radii, the mismatch of the aperture sizes will lead to much larger f_DM differences than those found for the simple estimator mismatch ( vs at the same radius; Fig. 6). Here, we show , as might be adopted for modeling of observations, and , representing a simple option for simulations (where spherical curves of growth separating gas, star, and DM particles could be used to find both the composite baryon r_{1/2, 3D, baryons} within, e.g., R_vir and then ). For small B/T, is larger than , but for large B/T, the trend reverses (excepting the R_e, disk = R_e, bulge = 1 kpc case), and can be up to 50%–400% larger than as B/T → 1 (for R_e, disk = 2, 5 kpc, respectively). This example illustrates how, depending on galaxy structures, quoted “half-mass” f_DM values can be very different – but that this is primarily driven by the aperture radii definitions and not by estimator mismatches.