The effect you are seeing can be best visualized by rendering your particles with output resolution of 640x480 vs. 1280x960 vs. 2560x1920 etc. The particles are drawn as 2x2 (or 3x3) pixel splats onto your view, and hence look smaller and further apart as the resolution increases. The same effect is occurring as you increase the resolution of your shadow map.
Krakatoa skill mostly involves knowing how to manage the resolution of your shadow maps, and the density settings to get the lighting you require.