This is more of a tangent on Doubles drill but IMO my personal crackpot theory is that the low shots on Doubles aren't really what most people call "pre ignition push". It's a bit of a semantics argument but I think the difference is important.
When most people talk about preignition push, I think the generally accepted definition is that it means mistiming the recoil control push and going early, based on incorrectly predicting the timing of the shot breaking. Sometimes people conflate this with flinching, sometimes they make a distinction between the two, I don't know that it matters for the point I want to discuss.
Now, thinking abstractly about Doubles drill using that definition above, one might guess at a few plausible patterns of errors (pretend you've never shot Doubles so you don't know what usually happens).
1. If it's just the mistiming of recoil control, one might expect preignition push to happen equally frequently for all shots fired, regardless if it's the 1st or 2nd shot.
2. Perhaps there will be an increasing or decreasing trend of preignition push as you go further into an 8 round string, due to either getting more flinchy from shooting, or getting more acclimated to recoil.
3. Since you are only shooting pairs, and only have to control recoil after the first shot, maybe there should only be preignition push on the 1st shot.
Now having shot Doubles, I think 99% of shooters experience that the 1st round goes exactly where it's supposed to, and the 2nd round is where the problems happen. Given that this doesn't match any of the preignition push expectations above, I think it's really something else, which I call "post ignition over-pushing" for lack of a better term. It's kind of a nitpicky distinction, but I think it's important because it's really not a timing question (per my theory), it's a question of the magnitude of the push.