Didn't know if to post this on viewpoints or here. If it doesn't belong here, some mod feel free to move it.
Picture a graph with 9 bars, one for each E type. Depending on what happens to you, and how you react to it, during your first 5 years of life, the corresponding bar gets filled (according to what belongs to each of the types). The most filled bar in each centre will conform your trifix. The order is determined like this: the deepest fixation (the third fixation) forms first, because it was the first bar to be filled past the "cutoff point". The first fix (main E-type) was the second bar to hit the cutoff point, and the second fix, was the last bar to hit the cutoff point. Residual "bar-levels" on non trifix types, will give a "flavor" to the personality of the person.
I've termed the first fix "main mode", the second fix "auxiliary mode" and the third fix "hidden mode". So if I'm correct about this (this is the part I'm not totally sure of), the order it forms is: hidden > main > auxiliary.
I came up with this studying my own case. It might not behave the same with other cases. I'm trying to visualize if it lines up with another person I know. I welcome input on this, if you have any information. One trick is VI-ing and trying to remember what E-type predominated while viewing your childhood photo album (if anybody wants to aid this study).