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).