I wouldn't do either. I would talk to serious blueberry growers and see what they say, look for specialized information like Extension Service publications to see if there is anything about blueberries not sizing up. Otherwise all I can suggest is that maybe they aren't getting enough soil moisture during the summer.

And it's not a pollination issue, right? You do have several different blueberry cultivars planted near one another so there is adequate cross pollination?

Yes, three or four other types nearby.

They get drip line water twice a day. Another like bush (nearby) produces fewer berries, but bigger ones.

I will ask the extension service.

Thanks.