Contrary to what many coaches teach, lower is not better for every athlete. Some athletes do better with a knee level heel recovery, and some athletes are better off with lower recoveries closer to the ground. Some athletes exaggerate this to the point where they actually drag their toe on the second step (see Asafa Powell in the video above), but I wouldn’t recommend this as standard practice. Notice that the tactic doesn’t gain him any ground on Andre DeGrasse in the next lane over.
Generally speaking, stronger athletes can get away with a lower heel recovery, while weaker, more elastic athletes often prefer higher recoveries. In any case, the recovery of the swing foot shouldn’t be higher than knee height. At this extreme, it’s hard to get the foot back down to the ground fast enough to re-apply force.
To improve excessive heel recovery, drills can be incorporated where an athlete kicks over a cup or cone with the swing leg of their first step; however, be careful not to force any particular level of heel recovery on an athlete. By learning how to bound, or do Standing Triple Jumps, athletes will also learn a pattern that requires the shin to swing lower to the ground, and they can often apply this to their acceleration when needed. In this way, bounding drills often have great transfer to acceleration.