From what you have told us about your friend needing something behind the powder to bring it up even with the touch hole tells me that his pistol is poorly made, having the touch hole too far forward. When it is properly made, the touch hole should be right at the back almost flush with the breach plug. When it is located there, no matter how little powder you put in the barrel, the ball will not obstruct the touch hole. While I have not seen his pistol, I would assume that since it does fire, you may have misunderstood his reason for adding a second substance when loading. He could likely have been adding a filler on top of the powder, not behind it. Doing it this way, the added filler material acts to seal the hot gasses from burning through the patch. This can be helpful when using a thin patch.