I have same observations as Mr Bush.
I have placed beehives right next to sunflower field. 30 meters away. And I have watched the bees head in other directions to the clovers and alfalfas nearby. Walking in the sunflower field blooms I have seen the flowers loaded up with bumblebees and other wild/native bees, then the occasional honey bee. If I were to count I would likely come up with 200+ bumbles and other pollinators to one honeybee in the sunflowers.
Later when pulling honey off the hives there, the honey is high in the clover/alfalfa honey with some sunflower in it. An exquisite tasting blend!
By far the highest yields I have seen on hives equipped with scales, in good midsummer conditions is on CLOVERS: red, alsike, sweet. 11.4-11.8 Kg PER DAY ( 25 lbs per day).
Hope that helps!