As you'd know, certain older transport aircraft in the 20th century, such as Convair 990 or Tu-134 featured very distinctive, large anti-shock bodies situated on the trailing edge of the main wing so that the cross-sectional area transition/distribution of the aircraft would be more subtle and thereby reducing wave drag on the high-subsonic/transonic flight regimes.
What got me wondering though, is when designing a flap track fairing on an aircraft that doesn't feature any dedicated anti-shock bodies, how much of it is the result of consideration regarding the area rule/wave drag, as opposed to considering other drags like profile drag?
I know that the flap track fairings as found on most airliners are not designed to act as an anti-shock body, but thought that it would be valid to assume that it will at least have some effects in terms of the area rule and if so, there might be some consideration put into the design regarding it.
It seems like the more recent design trends like in the case of A380, A350XWB and B777X are such that they are trying to make the flap track fairings as small, slim and streamlined as possible and thereby minimize their aerodynamic effects and instead feature other aerostructures, such as an extended wingbox fairing that trails longer behind the actual wingbox to compensate for decreasing cross-sectional area. Are these observations correct?
If it is correct, how does the question in the title apply for older airliners/transports which didn't feature such designs like an extended wingbox fairing? Would it be safe to assume that flap track fairings had a bigger role in achieving smoother transition of cross-sectional area distribution for those older aircraft?