Appeal against non-award of PIP mobility component

My husband recently migrated from DLA to PIP. He suffers from bipolar affective disorder, post-traumatic stress disorder, and chronic anxiety. Thanks to his CPN and also to the excellent guidance provided by Benefits and Work, he was awarded the enhanced rate of the daily living component but not (what a surprise) the mobility component. Thanks to the recent rushed through change in the law, the fact that going out alone causes overwhelming distress no longer counts. however, we did hope that for Question 13d the fact that my husband can't plan or follow a route on his own (confirmed by his CPN) would count for something. Nope! And of course the Mandatory Reconsideration changed nothing. We are going to appeal, even though there is (to my knowledge) no case law re the new legislation. My queries are these:

Does anyone have any idea what a decision re question 13d would be based on? I can't find anything in the online guidance for decision makers re this.

My other question concerns a tribunal hearing. I have considerable experience with tribunals, having been a adjudication officer in the old Department of Employment, and having helped and represented my husband at several tribunals (100% successfully). However, during the last tribunal we attended, my husband broke down and was so distressed that he was unable to take part; the tribunal were very kind and supportive and allowed me to speak on his behalf. His PIP was awarded without him having to attend a face-to-face assessment, because he would find it overwhelmingly distressful (his CPN backed us up on this). It is therefore out of the question for him to attend a tribunal hearing personally as he would simply break down again and his already fragile mental health would be at risk. In the dim and distant past, in my capacity as amicus curiae (friend of the court) as an Adjudication office, I attended a number of tribunal hearings where the claimant was not present, and as either represented by someone or was unrepresented. In either case the tribunal did their best with the information available to them. I am in a better position than an outside representative would be to speak on my husband's behalf at a hearing, as I am his registered carer and know his condition and how it affects him inside out, so to speak. Does anyone have experience of recent tribunal hearings where only the representative, and not the claimant, was present?