Prolly too late for the OP since I assume he's already dosed but:
I like to think there are two kinds of flips. In the first kind, you take a moderate to strong psychedelic dose, wait till you're feeling it, and then take a moderate dose of MDMA either shortly before or right as you start peaking. In the second kind, you dose so the MDMA hits you first, and take a higher dose of MDMA and a more moderate psychedelic dose.
Basically, with the first kind, you start by getting into a 'tripping mindset', and then once you're already tripping you get this amazing burst of euphoric, loving positive energy from the MDMA. With the second style, you roll really hard, and then you enter your trip already in that wonderful, open, loving mindset of MDMA. Some people also find it extends the duration of the MDMA but IMHO that's just the psychedelics taking over and producing similar effects.
Basically, the decision to me boils down to how bad of 'the fear' you get and how unpleasant the comeup is of the psychedelic. If you're totally comfortable taking high doses of it to begin with and have no trouble getting in a good mindset, taking the psychedelic first and then adding the MDMA is the best way to maximize the intensity of the peak effect, IMHO. The MDMA first technique is really handy if you have trouble getting in a good mindset for a trip. If your mindset is totally wrong before a trip, you might have a bad trip, or you might barely trip at all. MDMA first puts you in the perfect mindset to counteract any fear and come-up anxiety and helps avoid getting stuck in thought loops and the like.
I think I've said the same thing about 5 different ways now, but I wanna finish with one simple rule of thumb from my own use (not saying anyone else should or should not adopt the same policies):
If I want a long, intense trip like a strong acid trip and I want to add MDMA to that experience, definitely psychs and then MDMA so you're into your psychedelic peak when the roll hits.
If I want a shorter-lasting substance like psilocin, especially if I'm worried I might not be in a perfect mindset to have a productive trip, I'd consider MDMA first. It doesn't give as much of the intensity of lining up the peaks, but it allows the trip to start from "mdma loved up" instead of your normal baseline, which can really help direct you to a productive trip.