I've not combined sunflowers but had some combined for me.  The fact that the heads hang with the berries down also probably helps on the moisture content of the seeds when there is snow and well below freezing temperatures.

Too bad they are not worth much now.  Neighbor said this morning he can't afford to pay what it would cost me to haul them to market for him.  I'm glad he found someone who will do it for less than $1.30 a running mile without a return haul.