That Wasn't So Hard:
I don't know why I dreaded this, it wasn't so hard.
I figured out the secret of layering strakes ( Contoured planks on a frame ) and where I have previously gone awry with this sort of construction. What you need to do is install backing strips to the inner surface of the main planks so you have something to glue the filler planks.
Previously I attempted to add the filler planks without backing. I used 1,0 MM X 6.3 MM styrene for the planking which moulded easily but was still thick enough to take a finishing sanding.
The image above shows the upper nose segment rough sanded and the lower segment with the plans in the rough unsanded stage.
The image below may make the explanation clearer.
Once I have the muzzle segments completely rough sanded I'll wet sand the whole cowling.
I never use filler such as Greenstuff and Milliput because it looks like hell ( Especially the Green Stuff ) and you have difficulty gluing additional styrene to the foreign surface. Plus flaws in the contours are difficult to see until the surface is painted.
Anyway, "Onward and upward" as the saying goes I'm quite pleased with the result.