I probably should not comment since I use over-the-ball lube instead of felt wads in my cap guns, and simply coat the bottom of the bullet with lube for black powder cartridges. But I am trying to imagine how a lube wad works, considering the dynamics of pushing a projectile down the barrel.
Pressure is going to go sky high when the powder burns, mashing the felt wad against the base of the projectile. If I am imagining correctly, it seems to me that a low density felt with lots of lube is going to extrude more lube out when it is mashed than a hard wad. So I think a low density mashable wad would be more effective, would it not?