Thanks everyone, whilst I have not got the rib shading exactly right, I agree with many on here that the WNW lozenge is too bright.
My process is as follows:
Paint and smooth down the wing surface (black this time) and klear to get a glossy finish. Apply lozenge strip using decalfix and hairdryer. Trim and apply rib tapes, again using hairdryer to set. Then add the crosses and any stencils, and apply two coats of klear to seal the decals and protect against the varnish. Then I brushed on the mattcote, mixed with humbrol thinner so as not to overdo the matt effect, brushed between the rib tapes (not quite as accurately as I would like, but ok - another time I would mask the rib tapes).
When dry, drybrush on some weathering powder - black pastel rubbed on sandpaper here - but perhaps a smoke shade would be more subtle.
Chris, I did not apply any further coats to seal the powders, they bed into the matt surface sufficiently. Even carefully brushing a thin coat of klear over (next day) would not remove the powders, well maybe some, but most would be left.
I am still loathe to spray klear or varnish in case I over do it or get the orange peel effect.... I will try on an other model as the mattcote would work well with an airbrush, as would klear.