Generally, when you do a reverse diet, you want to make sure that you are in a calorie surplus every day. This allows your body to receive the constant signal that it is getting more food than it needs, and this is what stimulates an increase in metabolism ultimately.
So if we allowed drastic high days and lower days, you would have several days where you’re eating way below your needs and others where you’re eating far above.
In theory, this might not be the optimal stimulus to increase metabolism. By limiting the magnitude of your high and low days, we can ensure that your calories never drop below maintenance level. This will keep you eating either at or above your needs on a daily basis, which may maximize the effectiveness of your reverse diet.