  Significant progress has been made recently in our understanding of the
structure of stellar magnetic fields, thanks to advances in detection methods
such as Zeeman-Doppler Imaging. The extrapolation of this surface magnetic
field into the corona has provided 3D models of the coronal magnetic field and
plasma. This method is sensitive mainly to the magnetic field in the bright
regions of the stellar surface. The dark (spotted) regions are censored because
the Zeeman signature there is suppressed. By modelling the magnetic field that
might have been contained in these spots, we have studied the effect that this
loss of information might have on our understanding of the coronal structure.
As examples, we have chosen two stars (V374 peg and AB Dor) that have very
different magnetograms and patterns of spot coverage. We find that the effect
of the spot field depends not only on the relative amount of flux in the spots,
but also its distribution across the stellar surface. For a star such as AB Dor
with a high spot coverage and a large polar spot, at its greatest effect the
spot field may almost double the fraction of the flux that is open (hence
decreasing the spindown time) while at the same time increasing the X-ray
emission measure by two orders of magnitude and significantly affecting the
X-ray rotational modulation.
