A grade level answers at A-level tend to travel around the main facets of the question but do not excite the examiner. As i'm sure you've been told again and again, examiners do not spend long on an individual script! In order to grab their attention you must draw on materials and ideas that other candidatesa are not using. I'm sure you've been told that this can be done through the use of a broader range of case studies. This is correct! However it is not just about their inclusion but HOW you use them. WHilst A grades can be attained by tagging them on to a point, for an A* they should drive the point. Through the use of persuasive language and continual referrals to the case studies, they are no longer stand alone points but rather a key component of your argument. This demonstrates that you know them well and are able to manipulate information not just reference it.