I don't know what your soaking cleaner is, but since you have a borescope you don't need to rely on color indicators, so you can take advantage of KG-12, which doesn't change color much (gets a little bit darker orange) but eats more copper faster than anything else I've experimented with, Boretech's Cu++ coming in second. Both beat the pants off the ammonia-based copper removers.
As to prevention, the bore can be firelapped. Even doing this very lightly just to dull the worst grabby edges of the tool marks in the bore can help. However, another possibility is adding
Tubb Dust to your powder. It is hBN that coats the bore to make the surface unable to hold onto copper well. It's a little messy, but it works. I've had success with other bore treatments, but this one is self-renewing with every shot and tends to eliminate first-shot POI change, as well as reducing copper fouling. You add about 12 grains of it to a pound of powder and mix thoroughly.