If we consider all researchers to be vertices in an undirected graph, where edges indicate a recent working relationship, then the pool of ideal reviewers looks somewhat like a donut centered over the author(s). Roughly it is the reachable(n) part of the graph minus the reachable(m) part.

Some of the most interesting parts of this readership have no direct links to the author(s) as they have not commenced their piece of work yet, so we must assume they are located near to their advisors within the graph.