Each season I see many small aborted berries at harvest time. While all of the above factors can affect fruit set and size, in my opinion it is not any of these that limits fruit set and production. My research clearly showed that most of the carbohydrates that support fruit set and growth come from leaves on the current season growth above the fruit. Good overall management will give you the best chance of setting and keeping as much fruit as possible. Having enough, but not too much N is important.
Good pollination is critical, as is frost protection.
But none of these individually will increase production. In my opinion this phenomenon is not a fertility issue. In my opinion this is not strictly a fertility issue, but is a sign of stress. I have also seen it in hot periods. We typically don t see the symptoms in spring or in cool years.