An x-ray tube assembly is provided comprising a tube casing assembly including a plurality of vertical mount posts. An insulator plate is mounted to the plurality of vertical mount posts such that the insulator plate can translate vertically on the posts. A cathode assembly is mounted to the insulator plate and generates both an eccentric moment and a vertical expansion in response to a cathode power load. A semi-compressible element is positioned between at least one of the vertical mount posts and the insulator plate. The semi-compressible element becomes incompressible at a cathode power threshold such that the vertical expansion is translated into a correction moment countering the eccentric moment.