Consider this a lesson learned working at this entirely too hard to get that many rounds in that kind of shape. IMO nothing good can come of shooting 9 out of 10 of them.
In my experience with handgun rounds, I use three steps to set up the flare. I use the feel of the press, a visual that the mouth is belled, and if I am really trying to save hard working the case the finger feel (or measure with a caliper) of the case after the stroke.
Use one case for this step, lower the ram to just touch a case with the die, raise ram and screw in third way turns, repeat raise-turn-lower, until a bullet will just click into it with a slight rocking, jiggling motion then turn it just an eighth more for smooth entry. On the next case you can literally feel the mouth bell open the correct amount.