https://doi.org/10.1093/mnrasl/slac053

They have simulated 21-cm light-cones using 21cmFAST between redshifts 7.21 and 8.90 assuming saturated spin temperature. Their astrophysical model after Greig 2015 has 3 parameters:

1. $\xi$: ionizing efficiency,
2. $R_{mfp}$: mean free path of ionizing photons within ionizing regions, and
3. $T_{vir}$: minimum virial temperature of star-forming haloes.

Their fiducial model has $\xi=34$, $R_{mfp}=15$ and $T_{vir}=log(50000)$, and the change in the HI fraction $\Delta \bar{x}_{HI} = 0.68 - 0.26 = 0.42$. The density field is computed on a $512^3$ grid and the astrophysics is simulated on a smoothed $128^3$ grid.