Furthermore, you mentioned, "That last sentence is key to understanding why Deformable and Rigid behaviors would give different reaction forces, the force is being applied to fundamentally different structures: one is stiffer than the other.", but the additional stiffness that is being added due to the Rigid behavior is still going to be equal between the two bodies, right? So ultimately, there is no difference between these two bodies because we are adding the stiffness equally in both. So it shouldn't change the reaction force results, isn't it? Anyways, we both agree that using hand calculations by using the concept of statics will not give correct reaction forces even if we are doing a linear analysis, but if the scoping is Rigid, right? For Deformable, yes it would. But for Rigid, I don't think so.