In a situation where there is a >400 ranked school and in throughout several course the top 3 people lets say 'x', 'y' and 'z'are pretty close in the internal assessment, say 92,89,87 respectively, and then the rest of the class is 77-60. If 'x' gets 93, 'y' gets 90 and 'z' gets 89 in externals...