Apologies for not replying earlier, I've been travelling a lot over the last week.
I've been trying to find the notes I was given on the operation by Columbia Helicopters. I was looking at chartering the BV 107's for a similar operation several years ago.
I guess the answer to how long the line is, is, "It's pretty long". As regards hieght, well, it certainly doesn't make sense to be 10 or 20ft AGL as the picture suggests!
If I find my notes I'll post them, makes good reading.