Forgive the lack of link to back this up, but also doesn't MDMA itself affect how MDMA is metabolized? Like a redose can slow it down somewhat? I might be wrong on this.
no, your right. mdma inhibts the enzymes that break it down. the effect starts to really be noticable once you go over 1.5mg/kg (ca. 100mg for a 70kg person). then the concentrations of mdma in the bloodstream rise at a much higher rate than before with a small increase in dose. if you took it as a single dose or as a redose shouldn't matter much, but this is the reason for the recommendation of redosing at most half the initial amount.