Sets the exponent (1-15, default 9) WRED uses to calculate the average queue length for this specific priority entry, but only takes effect when the parent group's type is 'queue' -- letting each queue within a queue-based WRED group have its own averaging exponent instead of sharing the group-level one. An admin uses this for finer per-queue control of WRED's reactiveness when the group is organized by queue rather than by header field. It is indexed by group index, content index, and content sub-index.