Hi Ben,
Are you saying that you are getting similar curves for wavescans compared to MAN intensities plotted as a function of spectrometer position (for a given average Z)?
If so, that would be as expected because the MAN calibration curves (bgd intensity vs. average atomic number or Z-bar), are simply attempting to predict the continuum intensity at a given spectrometer position (for a range of sample average Z).
And yes, background intensity as a function of spectrometer position is exponential. Or perhaps I am missing something you are saying? Can you explain in more detail?