I have done some experimenting with reduced loads and fillers. I have found best consistency when there was a separator between the powder and the filler. Imagine a case filled part way with powder, then part way with filler, then a bullet. You have to compact the filler or the filler and powder will mix. Happens with dacron, cream of wheat, corn meal, plastic shot shell buffer, etc.
For my reduced loads in 357 brass, I use a small wad cut from the foam trays you get in your grocer's meat department. I have modified a fired brass by enlarging the flash hole. I have a modified nail with the sharp point removed and the head just a little smaller than the 357 case. I put the nail, point first into the case and the main shaft of the nail comes thru the flash hole. Head of the nail is inside the case and is stopped at the flash hole. I now use this brass, like a cookie cutter, to cut out circle "wads" of the foam. The nail pushes the cut wads out of the case. These little wads are placed on top of my powder charge. In my loads, I have found no additional filler is really needed. Standard deviations go down and no signs of the wad in the barrel or in the discharge. I don't know if it disintegrates when the powder flashes or what, but it is gone with no added pressure like you get from a fiber wad. In your loads, depending on case capacity, you may need to add a filler on top of the wad. Wad just keeps the filler and powder from mixing and you get a better SD over the chrono. I have never heard of a filler that can reduce leading.
Just my $.02.
Steve