The problem is the mold and getting too hot. I had that 3" bait and the more I shot in succession the more the dents became worse. If I picked the mold up stone cold and shot it three times, no sweat. As soon as the mold took some heat the dents began and nothing would get rid of them except cooling the mold down to a cold state.
Topping off the sprue was futile. Leaving the baits in the mold longer only worsened the problem. Shooting cooler plastic didn't cut it. I'm of the opinion that hanging the baits won't help any either.