Cumulative distribution function curves of the kHz QPO emission radius r, as well as the corresponding S_z values, for (a) Cyg X-2 (S_z  ∼   − 0.09−1.13, r ∼ 17.4−21.5 km), (b) GX 5-1 (S_z  ∼  0.67−1.25, r ∼19.0−27.6 km), (c) GX 5-1 (S_z  ∼ 0.12−1.10, r  ∼  19.3− 28.7 km), (d) GX 17+2 (S_z  ∼  0.08−1.45, r  ∼  16.6− 23.4 km), (e) GX 17+2 (S_z  ∼   − 0.32−1.76, r ∼ 16.6−24.1 km), (f) GX 17+2 (S_z  ∼  0.16−1.16, r ∼ 18.0−24.0 km), and (g) Sco X-1 (S_z  ∼  1.25−2.09, r  ∼  16.1−17.0 km). The ranges of r that correspond to NB (S_z  ∼  1−2) are indicated in the shaded areas. (h) The CDF curves of all the kHz QPO emission radii that correspond to the HB (S_z  ∼   − 0.32−0.97, r  ∼  17.4−28.7 km) and corresponds to the NB (S_z  ∼  1.01−2.09, r  ∼  16.1−19.9 km) by combining the r values in diagram (a) (Cyg X-2), (c) (GX 5-1), (e) (GX 17+2), and (g) (Sco X-1).