Thanks for your feedback BJC. Yes, I tried to get some computer generated images, but couldn't find anything which would double and quadruple the distances accurately. Surprisingly, most of the replies are very positive so far, but of course it is early days yet, and in general the people who have already answered the survey have, like you, some expertise in this area.
For anybody who hasn't done the survey yet - the images and descriptions are on page 2 of the survey, just fill in page 1 first. (the wrong way around - NOW I know!)
Gillian