  The aim of this paper to determine the locally densest horoball packing
arrangements and their densities with respect to fully asymptotic tetrahedra
with at least one plane of symmetry in hyperbolic 3-space $\bar{\mathbf{H}}^3$
extended with its absolute figure, where the ideal centers of horoballs give
rise to vertices of a fully asymptotic tetrahedron. We allow horoballs of
different types at the various vertices. Moreover, we generalize the notion of
the simplicial density function in the extended hyperbolic space
$\bar{\mathbf{H}}^n, ~(n \ge 2)$, and prove that, in this sense, {\it the well
known B\"or\"oczky--Florian density upper bound for "congruent horoball"
packings of $\bar{\mathbf{H}}^3$ does not remain valid to the fully asymptotic
tetrahedra.}
  The density of this locally densest packing is $\approx 0.874994$, may be
surprisingly larger than the B\"or\"oczky--Florian density upper bound $\approx
0.853276$ but our local ball arrangement seems not to have extension to the
whole hyperbolic space.
