I do not know of any studies but from our experience I would say that it would depend on several variables such as, lay of the land, abilty or person planting, number of out croping in fieids just to name a few. We have six,eight and twelve row heads to match our customers planters because losses would be way to high without combine being right on the planter. I do know of regions in some states where harvesters do not have to match up because of flat fields and auto steering tractors letting farmers plant with the inch.