Step file of BPM received from Igor, imported into CST, cannot run eigenmode solver with lossy materials.
Recreated the geometry which allows scalability and can now export as a stl file for GdfidL. (It is also rotated 45 degrees about z axis to make positioning ports in GdfidL easier.
Ran eigenmode simulation of the original geometry and got the results shown below. With the dipole mode polarisations highlighted.