Volume velocity ratio with a monopole model for various cases presented in Figure 2. (a): the solid line represents each of the 3 secondary sources of the case 2 while the dashed and dotted one represents each of the 8 secondary sources for the case 3. (b): the dashed line represents the secondary source placed in front of the primary one and the dotted line represents each of the 8 secondary sources placed on the ring, both for case 5 without and with (same curves with circles) regularization with β = 200.