Thanks Guy. You're right. I've been aware of this from my very first satire, and have put up with it, rather than make any attempt to solve it. I've used the slightly more shadowy (almost reverse) lighting on the interviewer as an attempt to make as big a difference between the two roles as possible. The excessive shadow right at the start is a result of this. Next time I'll have a look at a reflector to fill light that position. The problem is I am wanting the shadow when I turn to address the interviewee.
One other issue I had this time was that I used one of my Lowel prolights with a snoot on as a fill light. It worked, only in the interviewer position there was a small circle of light from it that played around on the back side of my left glasses len's, and was very very distracting. I normally do about four takes of every line, then pick the one that is best for my purposes, but this time I had to discard about half of them because of this moving light spot. This was even though in all other respects the take was better. If the light had been a few inches more to the front I wouldn't have got it! You can just see it in a couple of bits but it's nothing you would notice.