The Lg phase has been demonstrated to have unusual stability and precision of relative scaling with the global mb or yield of nuclear explosions on a path by path basis. However, Lg scaling slopes with magnitude for different propagation paths are often quite different, an unexplained effect which complicates nuclear monitoring procedures. In this study, both data analysis and numerical simulations are used to explore the factors influencing Lg scaling. Digital seismic data from broadband stations in Eurasia for explosions at the former Soviet Union nuclear test site in Balapan are analyzed. The data suggest that yield scaling of the source spectrum, combined with frequency selection properties of propagation on each path are responsible for the observed variations in scaling slope. Loss of high-frequency energy by attenuation causes high scaling slopes along some paths. Variations in site effects and instrument responses may also contribute to the scatter of Lg scaling slopes. Numerical simulations, used to calculate synthetic scaling laws, support these inferences.