Fat cells don't physically move... The net effect is that it seems like fat is being moved over time, but it just gets absorbed from the old male areas and new fat gets put down in the female areas as our metabolism changes, and as our weight fluctuates naturally over time.
With me (and i think most others on HRT) any fat I seem to lose seems to drop from the old male areas first; if I gain it, it gains on the feminine areas first.