I'm sure it was based on a blog by a NATs controller.
The point they were making was that to get the absolute maximum efficiency from a 3rd rw you would be looking at a continous straight in parallel descent but with the straight in model starting at 18k. The impression I got was not one of closing the Microwave from left or right but actually being already lined up. I assume this compresses traffic on the glide.
The only article I could find is this which does indeed quote the model Dave Reid described but the blog I read definitely referenced this other model.
If you can get past the AirportWatch brigade this seems to be the model but the diagram I saw did specify the 25 mile+ long approach.
http://www.airportwatch.org.uk/2016/...fer-passengers