FS, I'm happy now that I understand the concept well enough from a layman's POV. What I think I was worried about all along was the idea that in some way the *whole* cross-section of the a/c contributed to the area calculation, and I couldn't quite see how that worked in the case of a/c components widely separated laterally. Whatever the issues regarding wing profiles (and I think it's more a case of me confusing the issue here rather than you
) it seems clear to me that my worry was groundless, and that calculations concerning wings can in general be kept separate from calculations involving the fuselage. (Probably best at this point to resist any temptation to correct this view, provided it's not complete balderdash!)
Thanks for your help. I may come back some time with a query on another of the many things I have trouble with in aviation theory
.