Finally sorted out, phew.
Checklist done as follows
Insert new cable, check height, alignment, movement. of FD – Adjusted where necessary, dropped approx 2mm
Route cable correctly (as per dove 1’s very helpful photo)
Clamp cable, with tension “hand tight”, set lower limit (while in 26F – 36R)
Although setting the H limit was a little unconventional.
Once I got it shifting to the 36, there was still too much tension to move the FD inwards using the H screw. So I had to drop it into the 26, half a turn on the H screw, then shift back to 36 to check. Repeat, repeat etc etc
Anyway, all’s well that ends well eh?
Cheers everyone, I was right on the point of buying a 1×12 groupset 😀