  We identify axion miniclusters collapsing in the radiation-dominated era and
follow them to redshift $z=99$ with N-body simulations. We find that the
majority of the densest miniclusters end up in the center of larger minicluster
halos at late times. Soon after their formation, the miniclusters exhibit NFW
profiles but they subsequently develop a steeper inner slope approaching
$\rho\sim r^{-2}$ on small scales. Using the so far most highly resolved axion
structure formation simulation with $2048^3$ particles we examine the structure
of previously studied minicluster halos. While the density profiles of their
subhalos are NFW-like we confirm that a modified NFW profile with a steeper
inner slope provides a better description for minicluster halos with masses
above $\sim 10^{-12}\,M_\odot$. We show that miniclusters with a higher central
density might be in contrast to pure NFW halos dense enough to induce
gravitational microlensing. Likewise, more compact minicluster halos will have
immediate implications for direct and indirect axion detection.
