Recent Active Queue Management (AQM) mechanisms instantiate shallow buffers with burst tolerance to minimise the time that packets spend enqueued at a bottleneck. However, shallow buffering can cause noticeable performance degradation when TCP is used over a network path with a large bandwidth-delay-product. Traditional methods rely on detecting network congestion through reported loss of transport packets. Explicit Congestion Notification (ECN) instead allows a router to directly signal incipient congestion. A sending endpoint can distinguish when congestion is signalled via ECN, rather than by packet loss. An ECN signal indicates that an AQM mechanism has done its job, and therefore the bottleneck network queue is likely to be shallow. This document therefore proposes an update to the TCP sender-side ECN reaction in congestion avoidance to reduce the FlightSize by a smaller amount than the congestion control algorithm's reaction to loss. Future versions of this document will also describe a corresponding method for the Stream Control Transmission Protocol (SCTP).