Making us information consumers too soon would spoil our potential as information suppliers later. Finally, if probes mutate as they replicate, they may change too much and ETIS may be cautious about sending out probes to begin with. Argument over which radio frequencies to monitor continues. Communications traffic carried on narrow, coherent, directed beams would be undetectable. We may be considered dangerous, or they may already be in secret contact for similar reasons.
Most discussions center on the leading surface of the expansion.
However, population pressure, which is supposed to be driving the expansion, would likely cause conflict for resources within the planetary systems well inside the leading surface of the settled sphere. To take this into account a survival factor is assigned to a site. Eventually, R dominates and the expanding ring dies out like a circular grass fire. This should lead to cyclic waves of migration and colonization. Planets are settled, exploited and then abandoned.