Planetary Defense relies heavily on sophisticated computer models to simulate the outcome of different mitigation scenarios, including deflecting or completely destroying an asteroid. Many computer models incorporate different physics equations to represent similar material behavior. For example, many geologic strength models used when simulating asteroid deflection and disruption have a pressure-dependent yield curve built in (e.g. Collins et al, 2004, Harwell, 2025). There are differences in the yield curves, or how much deformation and stress the material can withstand before breaking, as well as differences in how that damaged and fragmented asteroid material deforms. The physics choices made when modeling each event can impact the simulated outcome. Here, we compare several effect different physics models used across two codes used to simulate planetary defense scenarios, CTH and PAGOSA (McGlaun et al., 1989, Weseloh et al., 2010). We discuss quantitative and qualitative differences in the simulated outcomes caused by modeling choices. We also discuss the implications of these differences within the planetary defense field.