The kind of peaking one runner might do depends upon 3 factors mainly:
1/His/her individual mental and physic reaction to peaking
2/what was been his training pattern
3/what run distance event he goes to compete
About point one. I deal with runners that when they start to reduce mileage and pace to peak, after 2 days with easy effort they start pain on legs. But it´s not such a wired unnatural abnormal as we might think at first glance. It´s something rational that if you reduce the muscular stimulus the muscles do try to adjust and sometimes ther´s some pain or just some muscle soreness.
In other cases the runner, knowing the responsibility and the task of the competition imagine that if he continues the process of hard training stuff also in the last few days before the run, he got the chance of some shape condition enhance at the last moment/minute, what is physically unproved but might be of some mental interest.
Other complexity is what´s the best type of peak for each individual ? We got a decrease from the first day of peaking to the last day of peaking. For example, one run on Saturday and he starts to peak at Tuesday. He does Tuesday – 40min easy, Wednesday – 35min easy, Thursday – 30min easy and Wednesday rest. Just an example. Well there are people that prefer the opposite, rest on Wednesday, and move to 30min easy on Thursday and Friday and 40min NOT SO EASY the day before the run. I did coach one runner that his best HM performances (1:04 HM pb) were done on Sunday morning, and the Friday (2 days before he did one day of rest and then the day before he loves to run 25k in about 1h30min what is not easy and not low volume !
About point 2. If you are doing 3-4 hard sessions a week or very hard/fast training with high frequency you need a different peaking kind eventually that one runner that does just 2 specific workout runs per week year round. The portuguese runners, Lopes, Mamede, Pinto, Castros, Guerra, Fernanda Ribeiro, Rosa Mota, if the run it´s not one marathon they do the last hard workouts till the 3 to 4 days prior the the run day and they only think about peak just 3 days before the run, be an Olympic run or the world cross country run.
About point 3. Of course that one marathon might require a different peak that one cross country or one track 1500m
Finally. Once again we got near the same conclusion. Ther´s some principles, but the peaking approach is as the training approach. Ther´s not a definitive and a single way that fits all kind of athletes. Therefore the peaking individualization is necessary.
Ps – by the information I got – that is limited of course – but I guess that US runners tend to use longer peak periods that is necessary. One marathon requires 1 week peaking and taper and all the rest 3 to 4 days. The pertinent question is how to do that peaking, not the need to more peaking days.