  The upcoming X-ray missions based on the microcalorimeter technology require
exquisite precision in spectral simulation codes in order to match the
unprecedented spectral resolution. In this work, we improve the fluorescence
K$\alpha$ energies for Si II-XI and S II-XIII in the code Cloudy. In
particular, we provide here a patch to update the Cloudy fluorescence energy
table, originally based on Kaastra & Mewe (1993), with the laboratory energies
measured by Hell et al. (2016). The new Cloudy simulations were used to model
the Chandra/HETG spectra of the High Mass X-ray Binary Vela X-1 previously
presented in Amato et al. (2021), showing a remarkable agreement and a dramatic
improvement with respect to the current release version of Cloudy (C17.02).
