In GNSS, the improvement of atomic clocks will lead to Phi/c^2 in relativistic gravitational redshift three to four decades from today. Research towards a relativistic positioning system capable of handling this expected accuracy is all based upon the Schwarzschild metric as a replacement of todays GNSS Euclidian-Newtonian metric. The method employed in this paper to determining frequency shifts between atomic clocks is an intermediate Minkowski-EEP approach. This approach is based on relating two atomic clocks to one another through a background ensemble of frequency gauged clocks, a grid. The crucial grid of this paper, the Free Fall Grid or FFG, can be related to the Ehlers-Pirani-Schild P-CP Weyl space formalism, when applied to a central mass. The FFG second order in Phi/c^2 redshifts are derived for static to static, static to satellite and satellite to satellite atomic oscillators and then compared to GR-Schwarzschild and PPN (Parametrized Post Newtonian) results.