You strive for these proportions. Not just for tradition and appearances sake, but for functionality also. I borrowed this graphic from Rosen’s Fly Fishing Blog, an excellent Bulgarian FF resource.

Classic Dry Fly Proportions @ Rosen's FF Blog (SB)

Proportion Matching

D = G = Е = 2 x C = 2/3 B

F = H = 1 1/2 x C

Excellent Fly Tying, Step by Step Tutorials