  The great power offered by photoionization models of Active Galactic Nuclei
(AGN) emission-line regions has long been mitigated by the fact that very
little is known about the spectral energy distribution (SED) between the Lyman
limit, where intervening absorption becomes a problem, and 0.3 keV, where soft
x-ray observations become possible. The emission lines themselves can, to some
degree, be used to probe the SED, but only in the broadest terms. This paper
employs a new generation of theoretical SEDs which are internally
self-consistent, energy-conserving, and tested against observations, to infer
properties of the emission-line regions. The SEDs are given as a function of
the Eddington ratio, allowing emission-line correlations to be investigated on
a fundamental basis. We apply the simplest possible tests, based on the
foundations of photoionization theory, to investigate the implications for the
geometry of the emission-line region. The SEDs become more far-ultraviolet
bright as the Eddington ratio increases, so the equivalent widths of
recombination lines should also become larger, an effect which we quantify. The
observed lack of correlation between Eddington ratio and equivalent width shows
that the cloud covering factor must decrease as Eddington ratio increases. This
would be consistent with recent models proposing that the broad-line region is
a failed dusty wind off the accretion disc.
