when you mention CAA, which CAA are you referring to? UK or Czech? I did my Performance exam in May with UK's CAA and what I found was that the margins are actually bigger than in Bristol question bank. I found the graph questions quite easy and passed the exam no problem. The graphs were also decent quality. If you see the answers that are so close to each other, perhaps it's worth appealing your results on the basis that the graph quality or resolution doesn't allow you to accurately identify a 30ft difference?