I don't use a filler in my repro revolver. I use 22 grains of fine blackpowder and it is accurate enough at 25 yards even though the ball is away from the rifling.
If I fill the chamber up with powder so the ball sits close to the rifling the accuracy is abysmal.

I don't know if a filler improves accuracy.I find that lower charges are better in most revolvers.

It may be that the ball has chance to stabilise at short range with the lower charge.