  Solar prominences observed close to the limb commonly include a bright
feature that, from the perspective of the observer, runs along the interface
between itself and the underlying chromosphere. Despite several idealised
models being proposed to explain the underlying physics, a more general
approach remains outstanding. In this manuscript we demonstrate as a
proof-of-concept the first steps in applying the Lightweaver radiative transfer
framework's 2.5D extension to a `toy' model prominence + VAL3C chromosphere,
inspired by recent 1.5D experiments that demonstrated a significant radiative
chromosphere--prominence interaction. We find the radiative connection to be
significant enough to enhance both the electron number density within the
chromosphere, as well as its emergent intensity across a range of spectral
lines in the vicinity of the filament absorption signature. Inclining the
viewing angle from the vertical, we find these enhancements to become
increasingly asymmetric and merge with a larger secondary enhancement sourced
directly from the prominence underside. In wavelength, the enhancements are
then found to be the largest in both magnitude and horizontal extent for the
spectral line cores, decreasing into the line wings. Similar behaviour is found
within new Chinese H$\alpha$ Solar Explorer (CHASE)/H$\alpha$ Imaging
Spectrograph (HIS) observations, opening the door for subsequent statistical
confirmations of the theoretical basis we develop here.
