In BC the two most prominent clinger nymphs are the Pale Evening Dun and Western March Brown. E. Hewitt in the 1930s experimented with flat body nymphs, but apparently they were not that successful -according to Terry Lawton's book where he quotes Gary Lafontaine. I know Oliver Edwards ties a flat heptagenid (clinger) nymph that is flat, but I think it is for the slow moving chalkstreams of England, which is not very applicable to the fast moving streams here in BC.
Although the natural clinger nymphs are 'flat' they do have a wide profile when drifting in the current. To give my nymph a wide profile I used a bead that are over sized relative to the rest of the fly. I also tie the rest of the fly to have a rotund profile. Using orange thread also adds a hotspot to the fly.
Originator: Danie Erasmus
Hook: #14 TMC 2587
Thread: 8/0 Black
Bead: 1/8 copper
Tail: Rusty brown pheasant tail
Abdomen: Rusty brown pheasant tail fibres
Ribbing: Small copper brown wire
Thorax: 0.02 lead wire and blood simi seal
Legs: Brown Stretch flex
Wingcase: Black holographic tinsel