Thank you for the comments. For a carbon seatpost the clamp is the correct way round. The instructions which came with the Campagnolo seatpost were quite clear that the gap in the clamp should not line up with the gap in the seat tube. The same advice came with a Fizik carbon seatpost I fitted on a friend's bike. Any other opinions about this are welcome. The Campagnolo Record seatpost came with a 31.6 - 31.9 clamp but this is too large for a Reynolds 853 seat tube so I used the Thomson clamp. I asked Dave to put the split on the front of the seat tube to protect it from road spray.
It is a custom frame for me. Dave Yates asked me about what riding I did and had a look at me on my other bike and told me what I wanted and he seems to have got it exactly right. The build, including the wheels, is by me.