  The soft excess in active galactic nuclei (AGNs) may arise through a
combination of relativistic reflection and the effects of a warm corona at the
surface of the accretion disc. Detailed examination of the soft excess can
therefore constrain models of the transport and dissipation of accretion
energy. Here, we analyze 34 XMM-Newton observations from 14 Type I AGNs with
the reXcor spectral model which self-consistently combines emission from a warm
corona with relativistic reflection assuming a lamppost corona. The model
divides accretion energy between the disc, the warm corona, and the lamppost.
The XMM-Newton observations span a factor of 188 in Eddington ratio
($\lambda_{\mathrm{obs}}$) and 350 in black hole mass, and we find that a warm
corona is a significant contributor to the soft excess for 13 of the 14 AGNs
with a mean warm corona heating fraction of $0.51$. The reXcor fits reveal that
the fraction of accretion energy dissipated in the lamppost is anti-correlated
with $\lambda_{\mathrm{obs}}$. In contrast, the relationship between
$\lambda_{\mathrm{obs}}$ and both the optical depth and heating fraction of the
warm corona appears to transition from an anti-correlation to a correlation at
$\lambda_{\mathrm{obs,t}} \approx 0.15$. Therefore, at least one other physical
process in addition to the accretion rate is needed to explain the evolution of
the warm corona. Overall, we find that a warm corona appears to be a crucial
depository of accretion energy in AGNs across a broad range of
$\lambda_{\mathrm{obs}}$ and black hole mass.
