Bllueberries - So. Calif coastal

Nursery told me cross-pollination was necessary. So I finally -- after waiting literally decades! -- got a pair of blueberry bushes that had been adapted to need much less winter chill, so can be grown in So. Calif coastal.
The "O'Neal" bush is loaded with big fat delicious blueberries
Its companion, "Sunshine", is also loaded -- but with tiny, miserable- looking berries that are drying up by the day. I am returning it to the nursery.
Questions:
1. Is "cross-fertilization" necesssary? Some of the sites I visited said yes; others said (AFAIK) that O'Neal was self-pollinating but would be better with cross.
2. If so, why can't it be between same varieties, rather than across varieties?
I am dizzy trying to evaluate the many varieties listed on the sites I visited. My #1,2,3, and so on requirement is FLAVOR. Prefer more tangy than mild.
Your input appreciated
TIA
HB
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Nearly all blueberries are self-fertile. But you will always get bigger crops/better harvests if you plant at least two *different* varieties. The explanation why is complicated :-) To grow blueberries successfully in your location, you should be selecting those with low chill requirements.......Southern highbush types. I'd recommend 'Jewel', 'Jubilee' or 'Sharpblue'. 'Jewel' is highly recommended for SoCal gardens and produces a lot of big tangy fruit.
I'm surprised at your problems with 'Sunshine Blue' - it is easily the most popular blueberry for home gardens on the west coast and highly recommended for SoCal as it is very tolerant of higher pH soils and has a very low chill requirement. It is entirely self fertile - one plant will still produce big crops of extremely tasty berries - and usually has no problems. I'd try again :-)
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