I'll attempt an explanation.
What I have pieced together from a number of sources, is that roughness in the leade can cause copper from the jacket to vaporize and go into suspension in the hot gas. It precipitates out further down the barrel as the gases cool. That's why fouling is usually worse in the last third of the barrel. The compounds in the coatings on copper fouling reducing powder react with the copper to keep it in suspension and let it blow out the end of the barrel.
I have proved to myself that lapping the roughness out of the leade will help reduce copper fouling. According to John Barsness, all Ramshot powders have a copper fouling reducing agent. I cannot confirm this from their web site or other literature but I plan to send them an email about it. Ramshot TAC is known to be such a powder. I use it extensively, especially in the .223, and find that fouling of all types is minimal.
I plan to try some of the new IMR powders myself.