I have played with lots of loads using fillers in the past, some with exceptional results. But... here's my humble opinion. I'm usually rushed for time, and prefer not to take loading steps that aren't absolutely necessary.
If you find that the 15.0g of Unique is too position sensitive for good accuracy without the fillers, I would simply move to a slower burning powder giving a slightly higher loading density, but the same approximate velocity. In this way you usually end up with a great load that doesn't require the filler.
For instance, if your load of Unique is position sensitive, then perhaps a similar charge of 800X would do the same job, but occupy more case capacity, thus making more uniform ignition possible without the need of fillers.
Just a quick fix to a situation that can occupy hours when loading fillered loads.
God Bless,
Marshall