In my experience the presence of the appellant actually tends to work against him because it tends to stifle proper discussion. Sometimes the panel of doctors need to freely air their thoughts without the "in-the-back-of-the-mind" warning signal that words uttered may be wrongly interpreted by the lay person listening. This free speech condition actually stimulates proper debating of the case at hand.
Having the appellant's own aviation medical doctor present tends to clear many of the problems that could have influenced the decision. Most appellants tend to force an emotional plea into the proceedings, whereas the panel only needs to evaluate the evidence at hand. Therefor; have your doctor in the meeting.
I am all for a legal representative being present to force the panel into making objective and legally sound decisions, since few doctors really consider the effect of the legal process, because they are not trained to think along legal lines.