The amplitudes that you see on the reflected waves on a field profile are affected by many things. Assume that corrections can be made for the spherical divergence of the wave, the transmission coefficients through the layers, inner bed multiples, etc. What remains are the spherical-wave reflection coefficients . Spherical-wave reflection strengths are not the same as the plane-wave reflection coefficients calculated in FGDP or by means of Zoeppritz  equations. Theoretical analyses of reflection coefficient strengths are always based on Fourier analysis. The equations in (25) provide a link between plane-wave reflection coefficients and cylindrical-wave reflection coefficients. See page 196 for going from cylinders to spheres.