I saw you deleted your part about movement, but that's what i wanted to try and explain.
With ffw, as soon as you pedalkick and the freewheel engages, your off. so the engagement you get is exactly what the freewheel provides.
With a freehub, when you pedalkick, the movement goes through the front cog, down your chain, to your rear cog, then the hub engages. So the movement from your feet is changed from the gear ratio you're running.
Does that help?