Hi Paul
You are free to argue whatever you want. The issue will be is what exactly was the assessor trying to assess and could it be reasonably done with someone having their coat on. There's things they could judge which I'm sure they would argue (and win) that having a coat on makes no difference.
It's up to you whether you want to mention about the prescription. Argue about things that will earn a claimant more points. Everything else can be deal with, in a couple of summary sentences at the end.
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
