It's not always possible to link the academic case directly to the extenuating circumstances.
Example 1: A child had a flare-up of eczema on the day of the test due to anxiety, and was constantly scratching. A distraction that wouldn't normally affect routine school work because the anxiety wouldn't be present and extra time would be given to complete the work.
Example 2: A child was very constipated and in discomfort during the test. Not sufficient to prevent them attending, but enough to present a distraction, and once again, it wouldn't be a problem at school.
(I hope I haven't inadvertently hit upon the actual "distracting ailment", but you get the idea.)
All you can do is demonstrate from the child's academic record that the performance on the day of the test was poor, given all the other evidence.
If there is a specific issue that you want to disclose privately, you can use the AppealsBox facility, described at the end of this post: viewtopic.php?f=35&t=35032
We can then advise you if it could be relevant to your case.