Combines loss per acre figures

I takes about 2 kernals per square foot (spread uniformly over the whole field) to make 1 bu_ac. Sounds to me like you're doing fine.

If the combine is not fully loaded you are going to get losses over the shoe_chaffer because there is too much air for the given load. Once the combine is full there is enough material on the chaffer to prevent excessive losses from too much air. So check the ground behind the combine when it is operating at normal speed and crop load. You are apt to see higher than normal losses when the combine is going into or out of the cut.