I have a 640D head and we are having problems with it feeding crop under the belts and then pluggin the belts. Not sure if it is pulling it under or if its shooting it across. Seems to be more like it is pulling it under. Anyone else have this problem on a 640 or 635D. I have tried speeding up the belts and slowing them down and i have also tilted the head forward more and it doesnt help. Any suggestion or answers? We are combining chest high winter wheat. Straw is from dry to green stem in the down spots.