$\pi_a$/$\pi_b$ respectively, not only from a geometric point of view, but also dynamically. This is evidenced by the excellent overlap of the distributions for different $N$ (bottom right panel of Fig. \[fig:inverseparticip\]).

Inactive sites enhanced transport
---------------------------------

The distributions of the IPR maxima reveal that for $N>5$ only a subset of the sites is substantially excited at the same time. In fact, the sites arranged in a backbone and those forming a pair or triplet possess a different dynamical role; while the former carry the excitation actively, sites closely packed together are never significantly populated by the excitation. Such a behavior emerges systematically for all system sizes, such that the pairs identified before for the case $N=6$ [@Mostarda2013] are just one example. In the following sections, we will thus refer to the backbone and to the pairs/triplets as to the [*active*]{} and [*inactive*]{} modules of the clusters.

![Efficiency loss upon removal of inactive modules as a function of the original efficiency $\epsilon$ for the clusters with $N=7$ and $N=8$. Error bars are calculated according to the standard deviation. All cases but $v_8$ are compatible with the pair effect found for $\tau_6$.[]{data-label="fig:efflossinactivemod"}](efficiencylossvertical_6.pdf){width="44.00000%"}

Removal of the inactive module results in a systematic 