  The decimation map $\mathcal{D}$ for a network of admittances on an
$n$-simplex lattice fractal is studied. The asymptotic behaviour of
$\mathcal{D}$ for large-size fractals is examined. It is found that in the
vicinity of the isotropic point the eigenspaces of the linearized map are
always three for $n \geq 4$; they are given a characterization in terms of
graph theory. A new anisotropy exponent, related to the third eigenspace, is
found, with a value crossing over from $\ln[(n+2)/3]/\ln 2$ to
$\ln[(n+2)^3/n(n+1)^2]/\ln 2$.
