Yes thats the one I referred to,
The pattern is my take on an American pattern called the "Coffin Fly". The dressing is
Tail, 4 x Moose mane hairs
Tag, Black peacock
Body, White Turkey primary herls
Wings Calf tail
Hackle Black or dark bkue dun cock
Hook Size 12 barbless Fulling mill 31836
It works really well when the spent Danica mayfly (as per your photo only your appears to be a sub imago) are floating down stuck in the film. It is slightly lighter than the real one but that helps you pick it out in the dusk, and as the fish are looking at the fly in sillouette in poor light I suspect thats why it works.
Check this out
Note distinct dark tip of tail and thorax.
Regards