Adrian, You can't win with this. A nice smooth sweep from the handlebar lever and down the timing side of the frame top tube, to drop down the saddle/ filter support tube on the drive side. Then it's back across over the frame lug for the gearbox top mounting, ready to be chafed on the gearbox cast lug. Depending on how long the cable is, you may be able to give more gentle sweeps, or even run under the gearbox top lug mount for a straighter cable run to the operating lever on the gearbox. Sometimes better to start at the gearbox and work back to the handlebars.
Swarfy.