Particles spawn in the right place relatively to an entity, however, they don't match its scale so it looks like the bigger entities have less particles relatively to the smaller entities.

6 Blazes. Scales are 1/8, 1/4, 1/2, 1, 2, 4 from left to right. The one on the very left looks like a flying living smoke itself and the one on the very right has too few particles.