We are developing regional-phase (Pn, Pg, Sn, Lg) tomographic attenuation models for Eurasia. The models will be integrated into the National Nuclear Security Administration (NNSA) Knowledge Base and used in the Magnitude and Distance Amplitude Correction (MDAC) station calibration for the development of regional seismic discriminants. Our current focus is on Pn, an extremely important phase in seismic event identification. Accurately accounting for regional-phase geometric spreading is critical for the development of useful attenuation models. It is particularly important for Pn and Sn waves because the propagation mode of these waves makes them more susceptible to upper mantle velocity structures and the Earth's sphericity, which in turn causes the geometric spreading of Pn (and Sn) to be dependent on frequency as well as on range in a complicated way. We conduct numerical simulations to quantify Pn and Sn geometric spreading in a spherical Earth model with constant mantle velocities.