  Simulating the distribution of cosmological neutral hydrogen (HI) during the
epoch of reionization requires a high dynamic range and is hence
computationally expensive. The size of the simulation is dictated by the
largest scales one aims to probe, while the resolution is determined by the
smallest dark matter haloes capable of hosting the first stars. We present a
hybrid approach where the density and tidal fields of a large-volume,
low-resolution simulation are combined with small haloes from a small-volume,
high-resolution box. By merging these two boxes of relatively lower dynamic
range, we achieve an effective high-dynamic range simulation using only 13% of
the computational resources required for a full high-dynamic range simulation.
Our method accurately reproduces the one- and two-point statistics of the halo
field, its cross-correlation with the dark matter density field, and the
two-point statistics of the HI field computed using a semi-numerical code, all
within 10% accuracy at large scales and across different redshifts. Our
technique, combined with semi-numerical models of reionization, provides a
resource-efficient tool for modeling the HI distribution at high redshifts.
