My opinion, PitchFlex would not be my go-to algorithm for drop tuning. The PitchFactor uses older technology, so you’re going to get some level of processing delay, no matter what algorithm you choose.
I would try using H910 / H949 for this, with similar settings. But in this case, Depth / Key fully clockwise to Modern, and Speed / Scale to either Normal (CCW) or Chromatic (CW).
You may prefer HarModulator, also with similar settings to my first reply. The difference here would be to remove the modulation (Depth / Key centered at 12:00).