Well, I tend to use about 2/3rds of the fruit in primary and then the final 1/3rd in either secondary or tertiary as that gets you a far "brighter" more fruity flavour (you'd be surprised how much of the flavour/aroma can be just blown straight out the airlock during ferment).....
Also, with blackberries, I invariably also add some steam extracted elderberry juice into the finished ferment, as it doesn't add too much to the fruit flavour but a hell of a lot of body, tannins and especially colour - blackberry can come out surprisingly light.......
regards
fatbloke