From my data, i kinda "felt" ( so i can be wrong and just placebo effect ) that the spike intensity depends on BaseDMG:
The higher BaseDMG is, the more values the distribution will have, the less "intense" the spike will be;
If using DMG1 weapon, distribution will have few values and spike immediately gets to very high %.

For determining q, why motenten's method wouldnot work ? you don't have enough parses ? (Note i've asked this question since my 1st post and no answer). I'm not sure i understood correctly the problem there...

And finally, i never ever said your model approach isnot "correct" in the sense of mimicing observed frequency parses, but i said this approach is deterministic, ie according to you, SE put this spike on purpose...
A non deterministic way is to use the definition of a pseudo RNG defined as Y=START+INT(RANGE*Generator), strangely its main signature is a spike at start, from there you can guess how it can be adapted to our problem, and this without using any parameter q or whatever. Think of this spike like an "artifact" occuring only when pDIF=1 is generated. An example of it is what Raellia posted at Mathy BG forum.
Saying this doesnot turn in any way your approach as "not correct", ok ?