Using Chandra HETG data we present light curves for individual spectral lines of Mg xi and Mg xii for EX Hydrae , an intermediate-polar type cataclysmic variable . The Mg xi light curve , folded on the white dwarf spin period , shows two spikes that are not seen in the Mg xii or broad-band light curves . Occultation of the accretion column by the body of the white dwarf would produce such spikes for an angle between the rotation axis and the accretion columns of \alpha = 18 \arcdeg and a height of the Mg xi emission above the white dwarf surface of \lesssim 0.0004 white dwarf radii or \lesssim 4 km . The absence of spikes in the Mg xii and broad-band light curves could then be explained if the bulk of its emission forms at much larger height , > 0.004 white dwarf radii or > 40 km , above the white dwarf surface , although this is not consistent with the predictions of the standard Aizu model of the accretion column .