Thanks for the information sent to the Appeals box. I like the tables and appendices!
The length is all right - what really matters is the attached evidence.
We would advise against mentioning character or positions of responsibility. They're not among the criteria for a successful appeal. Keep the focus on academic evidence - anything else is a distraction.
Marylou makes a useful point above. It's not usually going to be a strong argument (because it's hard to know who the 'sensitive souls' were out of all the children sitting the tests outside their normal environment), but with a score of 120, and the fact that this was in the second test, it's certainly worth a brief mention. I wouldn't say anything about it in your written appeal. Wait for the hearing, and just answer any questions as briefly as possible. In section B of the Q&As we advise:
If your extenuating circumstances are not too strong (in the sense that there isn’t any evidence at all to show that your child was affected), the best you can do is to appear reluctant to ‘offer excuses’, to let the panel drag the information out of you bit by bit, if the opportunity arises, rather than to build it up as a major issue. Understate the point, don’t overstate it, or you risk diluting your case as a whole.