Are you using a Cocktail Kingdom Coco Fine Strainer? If not, it may be worth investing in one, as it is better for this than most other fine strainers.
Nice cocktail. The wine provides a slight grape aftertaste. Nicely dry. This is a cocktail which will be greatly impacted by the quality and sweetness of the blueberries and the quality of the wine. Would recommend only making this when blueberries are in season and not being shipped from far way.