Deformable headforms can be used to make direct in situ intracranial strain measurements, however these physical models require significant refinement to ensure biofidelity. In particular, the boundary conditions of the brain-skull interface will influence the intracranial displacements and strains that develop due to a head impact event. This has been shown in half(open)-headform configurations in prior studies. In the present work, we investigate the response of a brain surrogate within a closed headform to the presence and absence of both a tentorium and a brainstem in different configurations to illustrate the effect of these boundary conditions on the intracranial strain fields. The present work uses radiographic techniques to investigate these headform design choices within the optically-inaccessible closed headform. The deformable headform was subjected to a series of impacts using a linear impactor, and the brain surrogate deformation was tracked using embedded radiopaque markers at an X-ray capture rate of 5,000fps. Digital Image Correlation analysis was used to calculate displacement and strain fields within the headform.