The effect of drafting increases as you move back in the peloton - at uniform speeds as the riders create a mass of air moving with the peloton. But, if the speed is uneven, accelerations tend to string the peloton out toward single file, that cloud effect vanishes and long after the leaders have sat up and are now resting, those at the back are still powering away at full throttle to bring the strung out line back to a peloton.