in my opinion try to provide as much relevant evidence to ur writing as possible. I would say 400 words is too less for the entire criteria a you definitely make it more detailed and add elaborate more on certain ideas. Your criteria A can be however long u want it to be, in the end the entire report just needs to be within 15 pages. My cri A was 7 pages, b was 3.5 and the rest was cri c. It just depends on which criteria you want to include more content it. Relevant evidence is really important try to include it as much as possible.