The magnetic field effect reduces the electron temperature for a given ion temperature, so reduces the x-ray energy loss. It is a quantum effect and Rider does not consider it. Calculations are only as good as the physics that go into them.
The Sandia z-pinch results, where they got ion temperatures of 280 keV and electron temperatures of 3.6 keV in an iron plasma is probably an experimental demonstration of the magnetic field effect. I am still analyzing those results.
