Everything works only half the time. Reliability occurs when two or three somethings pop off nearly simultenuously. Events in $NDX add spice to the S/R stew. I believe the great philosophe Y. Berra said "Sometimes you'll see things if you take the trouble to look."
What I recall from my earlier testing with the cash index (within the limited context of my own trading criteria), is that the additional info provided by the cash index would sometimes prevent me from entering what would have been a losing trade, and it occasionally prevented me from entering what would have been a profitable trade. I don't recall it having had incremental value for me. It just served as a not particularly discerning filter. And since my profitable trades are somewhat more profitable than my losing trades, the argument can be made that it had negative value for me. But again, that's just me.
Je repete: you are a momo trader. Momo is momo no matter what tools you use. $NDX IMO does not help in a momo decision.