The problem that you are experiencing is the inconsistency of moisture (or dryness). In the morning, your windrows contain a consistant amont of moisture throughout. In the afternoon's, the windrows are drying out causing feeding to be eradic due to dry material (probalby on top) and higher moisture material on the bottom. Those two opposing conditions can drastically change the feeding process of any combine. Increasing speed and adjusting stripper plates to a very slight tolerance will indeed help. However, the only reason I would run high on my feederhouse drum (corn setting) would be to alleviate increased shatter, which you are going to get anyway if the conola is dry, excess threshing always occurs in the feederhouse anyway. The higher the drum, the increased amount of material will be metered to the threshing system. I would rather have that a bit thinner to hedge the higher moisture swaths and potential rocks and debris that might be in the swath.