⁄ , the reservoir impedance of Equation 12 is larger than the reservoir impedance of a 5-spot (Equation ) by a factor of 4/𝜋. This 27% difference is due to the 27% smaller swept area of the "ID, Radial" and "TDF, Radial" solutions than the "TDF, Cartesian" solution. Thus, in Sec. 2.1.3, we use the potential functions to include the entirety of the reservoir area for an ID.