  We use the publicly available XMM-Newton archive to select a sample of 20
active galactic nuclei (AGN) known to exhibit reverberation signatures caused
by the reflection of X-rays from the corona off the accretion disc that feeds
the central black hole engine. Inverse Compton scattering by energetic
electrons, coupled with accretion disc fluctuations give rise to the highly
variable observed X-ray spectrum, the behaviour of which is still not fully
understood. We use 121 observations in 3 - 4 distinct spectral states for each
source and calculate the time lags as a function of frequency. We fit the
relativistic reflection model RELXILL and explore parameter correlations. The
known scaling relationship between the black hole mass and time lag is well
recovered and the continuum flux is coupled strongly to the disc reflection
flux. We also find that 1H 0707-495 and IRAS 13224-3809 are well described
using reflection and absorption modelling in a variety of flux states. The
reflection fraction is strongly coupled to the power law photon index and may
be linked to dynamics of the emitting region. The data reveals hints of the
power law evolutionary turnover when the 2 - 10 keV Eddington fraction is
$\sim0.02$, the origin of which is not fully understood. Finally, we report the
covering fraction is inversely correlated with the flux and power law photon
index in IRAS 13224-3809. These findings support recent studies of 1H 0707-495
where the covering fraction may contribute to the observed variability via flux
modulations from non-uniform orbiting clouds.
