The Differentiated Services architecture is a simple and scalable approach to provide Quality of Service (QoS) in IP Networks. Several studies have shown that the number of microflows in aggregates, the round trip time (RTT) or the mean packet size are key factors in the throughput of aggregates obtained using this architecture. In this paper, we examine the behaviour of one of the techniques suggested to improve fairness in a Diffserv network: the Aggregate Flow Control mechanism. We also propose two alternatives in the control overlay of this scheme and compare them with the original approach. Simulation results indicate that our proposed modifications improve throughput assurance and fairness requirements.