I hate muffins.....

I've just tried to make a batch of the blueberry muffins from my Hummingbird cookbook and they were a total disaster!  For a start my cases were too small which I didn't realise until googling the muffins and finding the Hummingbird 'hints and tips' pdf on their website - helpful if I'd seen it before but not really as it isn't part of the book!!
Secondly, why do all my blueberries sink?!  I've tried to put chocolate chips into their cupcakes before and they always always sink, as does jam, which I just assumed was because the sponge is so much lighter than a 'traditional' cupcake sponge, so why do my blueberries sink?  What am I doing wrong?!
And why don't they crack on the top like the ones in their photo??  It makes me cross that I can bake everything I've tried so easily, I've had cupcakes from their bakery before and mine were the same but with nicer icing (I don't like the American buttercream widely used), I HATE MUFFINS!!! 

I don't even want to put a photo of them up its too sad, I hate them, they have flat tops and the bottom is just a gooey blue mess.  What a let down.