  In this work we investigate the dependence of the escape fraction of ionizing
photons, $f_{\rm esc}$, on various galaxy and host halo properties during the
epoch of reionization. We post-process the TNG50 magneto-hydrodynamical
simulation from the IllustrisTNG project using the 3D multi-frequency radiative
transfer code CRASH. Our work covers the stellar mass range $10^6 \lesssim
M_\star/{\rm M_\odot} \lesssim 10^8$ at redshifts $6 < z < 10$. Adopting an
unresolved, cloud-scale escape fraction parameter of unity, the halo escape
fraction $f_{\rm esc}$ increases with mass from $\sim 0.3$ at $M_\star =
10^6$M$_\odot$ to $\sim 0.6$ at $M_\star = 10^{7.5}$M$_\odot$, after which we
find hints of a turnover and decreasing escape fractions for even more massive
galaxies. However, we demonstrate a strong and non-linear dependence of $f_{\rm
esc}$ on the adopted sub-grid escape fraction. In addition, $f_{\rm esc}$ has
significant scatter at fixed mass, driven by diversity in the ionizing photon
rate together with a complex relationship between (stellar) source positions
and the underling density distribution. The global emissivity is consistent
with observations for reasonable cloud-scale absorption values, and halos with
a stellar mass $\lesssim 10^{7.5}$M$_\odot$ contribute the majority of ionizing
photons at all redshifts. Incorporating dust reduces $f_{\rm esc}$ by a few
percent at $M_\star \lesssim 10^{6.5}$M$_\odot$, and up to 10\% for larger
halos. Our multi-frequency approach shows that $f_{\rm esc}$ depends on photon
energy, and is reduced substantially at $E>54.4$eV versus lower energies. This
suggests that the impact of high energy photons from binary stars is reduced
when accounting for an energy dependent escape fraction.
