The duct needs to be considerably further back than I thought. That is what you get when the manual shows a grainy photo with the caption "approximate position of cooling duct" with an obsolete muffler, which gives you no guidance at all. Anyway, this is the new position. Should have measured the coordinates for posterity but now it's in I am durn well not going to take it out again. Use eyeball instead.
Another problem is that the space between the footwells recedes and getting the ducting even a few cm further back is impossible. I dont't want to disassemble the duct to trim it so resort to the inelegant solution of sanding the footwells slightly. Looks worse than it is. But be warned- trim the back end of the CD 1 a few mm before riveting on CD 2 and 3.