  We couple the DELPHI framework for galaxy formation with a model for the
escape of ionizing photons to study both its variability with galaxy assembly
and the resulting key reionization sources. In this model, leakage either
occurs through a fully ionized gas distribution (ionization bounded) or
additionally through channels cleared of gas by supernova explosions
(ionization bounded + holes). The escape fraction is therefore governed by a
combination of the density and star formation rate. Having calibrated our star
formation efficiencies to match high-$z$ observables, we find the central gas
density to regulate the boundary between high ($>0.70$) and low ($<0.06$)
escape fractions. As galaxies become denser at higher redshifts, this boundary
shifts from $M_{h}\simeq 10^{9.5}\mathrm{M_{\odot}}$ at $z\sim 5$ to
$M_{h}\simeq 10^{7.8}\mathrm{M_{\odot}}$ at $z\sim 15$. While leakage is
entirely governed through holes above this mass range, it is not affecting
general trends for lower masses. We find the co-evolution of galaxy assembly
and the degree of leakage to be mass and redshift dependent, driven by an
increasing fraction of $f_{\mathrm{esc}}<0.06$ galaxies at increasing mass and
redshift. The variability in the escape of ionizing photons is driven by the
underlying variations in our dark matter assembly histories. Galaxies with $M_h
< 10^{7.9} ~ (10^{8.9})M_{\odot}$ provide half of the escaping ionizing
emissivity by $z \sim 10 ~ (5)$ in the ionization bounded model. On the other
hand, galaxies that purely leak through holes contribute $6$ $(13)\%$ at $z\sim
5$ $(15)$. We end by exploring the impact of two reionization feedback
scenarios, in which we suppress the gas content of galaxies with
$T_{\mathrm{vir}}<20000\mathrm{K}$ and $v_{c}<30\mathrm{kms^{-1}}$ residing in
ionized regions.
