I think maybe it would be good to trigger it at a specific time such as time of first transaction like comments or posts that way the RC's aren't wasted handing out to every single account. Perhaps as well if someone tries to transact but has insufficient resources it could trigger too? Spit balling here :D

A helpful constraint could also be accounts <60 days old too, that way they've had time to familiarize with hive and weed out those who just sell 100% of their rewards.