In my direct experience, grain size hasn't made much difference. Also, I use several kinds of very fine dusts/powders in my resin work and I've come to loathe t

In my direct experience, grain size hasn't made much difference. Also, I use several kinds of very fine dusts/powders in my resin work and I've come to loathe the whole category. They go everywhere at the slightest puff of air, stick to equipment and tools, etc. I already wear a mask, but with chemical (NIOSH magenta or olive) rather than particulate cartridges, so there's that too. Of course YMMV. Perhaps also relevant is that I tend to work mostly with low-viscosity resins because it's easier wrt bubbles and edge creep, but I've had the settling problem even with higher-viscosity formulations. Maybe some day I'll hit on a combination of materials and techniques that solves the problem. Just hasn't happened yet. Good luck!