I also feel like sometimes (rarely) it procs on the boss from prismatic crystal hitting the boss despite doing the ABx2 strat
That's just a matter of luck, personnaly it's the opposite, the MoD proc rarely on my PC, and my PC explosion on boss proc it on boss like 75% of the time.
For me, it's better to just forget that it exist for your pull and do AB*4, dump missile on boss, PC, spam AB on PC and AM on boss if MoD still up.
I prefer to have a better "worst case DPS" than a better "best case DPS". I don't care about ranking, not this early in HfC at least, so I personnaly prefer consistency than playing the lotterie. Our spec is already so much random and feel really RNG-punishing, so putting your pull on a 50/50% bet is just too much in my opinion.
And, doing big pull in Heroic is cool, but in true progress boss, where the fight will be longer than 2mn, your pull will have less and less impact, and having a better worst case DPS is for me more important.
And to finish, it feel so wrong to put your crystal whitout 4 AC ='(.