  The asymmetry in hard X-ray (HXR) emission at the footpoints (FPs) of flare
loops is a ubiquitous feature closely associated with nonthermal electron
transport. We analyze the asymmetric HXR radiation at two flare ribbons which
is thermal-dominated during a long-duration C4.4 flare that occurred on March
20, 2023, combining multi-view and multi-waveband observations from the ASO-S,
SolO, and SDO spacecraft. We find that the H I Ly$\alpha$ emission captures
similar features to the He II $\lambda$304 in both light curve and
spatio-temporal evolution of a pair of conjugate flare ribbons. The spectra and
imaging analysis of the HXR emission, detected by STIX in 4-18 keV, reveal that
the two-ribbon flare radiation is thermal dominated by over 95%, and the
radiation source mainly concentrates on the northern ribbon, leading to an
asymmetric distribution. To understand the underlying reasons for the HXR
radiation asymmetry, we extrapolate the magnetic field within the active region
using the NLFFF model. For 78% of the magnetic field lines starting from the
northern flare ribbon, their lengths from the loop-tops (LTs) to the northern
FPs are shorter than those to the southern FPs. For 62% of the field lines,
their magnetic field strengths at the southern FPs exceed those at the northern
FPs. In addition, considering the larger density, $\approx1.0\times10^{10}$
cm$^{-3}$, of the low-lying flare loops (< 32 Mm), we find the shorter path
from the LT to the northern FP enables more electrons to reach the northern FP
more easily after collisions with the surrounding plasma. Therefore, in this
thermal-dominated C-class flare, the asymmetric location of the flare LT
relative to its two FPs plays a dominant role in the HXR radiation asymmetry,
while such asymmetry is also slightly influenced by the magnetic mirror effect
resulting in larger HXR radiation at the FPs with weaker magnetic strength.
