No, particle size does not matter. Dyes are soluble in plastisol where as pigments are not. If you think of it this way:
-Pigments are like adding sand to water. Wont dissolve, wont move, the same as when you add it.
-Dyes are like adding sugar to water. Will dissolve, will migrate to reach equilibrium.
I know that is an oversimplification but it helps to conceptualize the difference between the two. Hope that helps.