Original text:
8.1. A sender needs to be responsive to notifications of congestion, such <del> as a packet loss or an ECN CE marking.  To enable a sender to respond to potential network congestion in a timely fashion, usually at least one acknowledgement per round trip is needed if there are unacknowledged ack-eliciting packets in flight.  A sender can accomplish this by setting the Ack-Eliciting Threshold to a value no larger than the current congestion window or the Request Max Ack Delay value to no more than the estimated round trip.  Note that the congestion window particularly but also the RTT are dynamic and therefore might require frequent updates if the selected value are close to these limits.  Alternatively, a sender can accomplish this by sending an IMMEDIATE_ACK frame once per round trip, though if the packet containing an IMMEDIATE_ACK is lost, detection of that loss will be delayed by the reordering threshold or requested max ack delay. Note that it is possible that the RTT is smaller than the receiver's timer granularity, as communicated via the 'min_ack_delay' transport </del>  parameter, preventing the receiver from sending an acknowledgment <del> every RTT in time.  In these cases, Reordering Threshold values other than 1 can be harmful, because it delays fast loss detection. </del>  A congestion controller that is congestion window limited relies upon receiving acknowledgements to send additional data into the network. less responsive to changes in the path's RTT, resulting in either delayed or unnecessary packet transmissions. <del> To limit these consequences of reduced acknowledgement frequency, a sender SHOULD cause a receiver to send an acknowledgement at least once per RTT if there are unacknowledged ack-eliciting packets in flight.  A sender can accomplish this by sending an IMMEDIATE_ACK frame once per round-trip time (RTT), or it can set the Ack-Eliciting Threshold and Request Max Ack Delay values to be no more than a congestion window and an estimated RTT, respectively. </del> A sender might use timers to detect loss of PMTU probe packets (Section 14 of QUIC-TRANSPORT).  A sender SHOULD bundle an IMMEDIATE_ACK frame with any PTMU probes to avoid triggering such

Reviewer comments:
We had similar text in the two sections, and the latter one was where the SHOULD was, so this consolidates the duplicate text into the Congestion Control section. This is intended as an editorial cleanup prior the the PR for

Revised text:
8.1. A sender needs to be responsive to notifications of congestion, such  <ins> as a packet loss or an ECN CE marking.  Decreasing the acknowledgement frequency can delay a sender's response to network congestion or cause it to underutilize the available bandwidth. To limit the consequences of reduced acknowledgement frequency, a sender SHOULD cause a receiver to send an acknowledgement at least once per RTT if there are unacknowledged ack-eliciting packets in flight. A sender can accomplish this by setting the Ack-Eliciting Threshold to a value no larger than the current congestion window or the Request Max Ack Delay value to no more than the estimated round trip. Alternatively, a sender can accomplish this by sending an IMMEDIATE_ACK frame once per round trip, though if the packet containing an IMMEDIATE_ACK is lost, detection of that loss will be delayed by the reordering threshold or requested max ack delay. Note that the congestion window and the RTT are dynamic and therefore might require sending frequent ACK_FREQUENCY frames to ensure optimal performance. It is possible that the RTT is smaller than the receiver's timer granularity, as communicated via the 'min_ack_delay' transport </ins> parameter, preventing the receiver from sending an acknowledgment  <ins> every RTT in time unless packets are acknowledged immediately. Additionally, Reordering Threshold values other than 1 can be harmful, because it can delay loss detection more than an RTT. </ins> A congestion controller that is congestion window limited relies upon receiving acknowledgements to send additional data into the network. less responsive to changes in the path's RTT, resulting in either delayed or unnecessary packet transmissions.  A sender might use timers to detect loss of PMTU probe packets (Section 14 of QUIC-TRANSPORT).  A sender SHOULD bundle an IMMEDIATE_ACK frame with any PTMU probes to avoid triggering such