I have the black one also and didn't like how loose it sits in there. So after much finagling about trying to find the right size weather strip or something to firm up the top, I ended up taking some foam and putting it under the whole cubby. It raised it up about 1/2" and now it's solid. Granted, there's a gap around it if you look, but no one has said anything yet.

I bought it just for the cup holder. Nice to have a bottle of water secure enough to open and not swinging around on the bars.