Just throwing out some info here, blueberries have almost no flavor, even when eating them they ar dull. So one would need a massive amount of fruit to get any noticeable flavor, but it's going to dissipate rather quickly. Now as far as finished flavor even the best commercial examples do not carry a lot of flavor but they have aroma. To achieve this use the berries as everyone had been
using but in the secondary, and right before kegging or bottling use a fruit extact. Use in moderation as it will add flavor not just aroma. Look at commercial beers, clear but a big blast of blueberry aroma, just not a lot of flavor. Wachusette uses up to 762 lbs. of fruit in their batches. Good luck brewing and I hope this helps a little bit.