A warm corona has been widely proposed to explain the soft excess (SE) in X-ray above the 2–10 keV power law extrapolation in Active Galactic Nuclei (AGNs). In actual spectral fittings, the warm coronal seed photon temperature (Ts) is usually assumed to be far away from the soft X-ray, but kTs can reach close to 0.1 keV in the standard accretion disk model. In this study, we used Monte Carlo simulations to obtain radiation spectra from a slab-like warm corona and fitted the spectra using the spherical-geometry-based routine thcomp or a thermal component. Our findings reveal that high Ts can influence the fitting results. A moderately high kTs (around 0.03 keV) can result in an apparent low-temperature and flat SE, while an extremely high kTs (around 0.07 keV) can even produce an unobserved blackbody-like SE. Our conclusions indicate that, for spectral fittings of the warm coronal radiation (SE in AGNs), kTs should be treated as a free parameter with an upper limit, and an accurate coronal geometry is necessary when kTs > 0.01 keV.

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