Length of cars matters more than length in sailplanes. There are not many cars under 13 feet long that can fit four people ~6'-4" tall, in relative comfort. My Scion xA does.
Sure frontal area matters, but if the Cd is lowered from X to Y, then that matters about 3 times more.
As for weight, a sphere encloses the most volume inside of the least surface area, and a cube encloses the next most volume for a given surface area. Less surface area means less metal, glass, and plastic. Elongated rectangles have more surface area for a given interior volume.
So, a longer length, lower height car with the same interior volume as another car that is shorter length and greater height; the longer, lower car will weigh more, all else being equal.
I fit much better in a Honda
Fit than a
Civic, and the legroom / headroom dimensions reflect this. Their interior passenger volume is virtually identical -- within 0.1 cu ft. The cargo volume is much larger on the Fit -- 8.6 cu ft more.
The height difference is only ~4" anyway; and the Fit is a little more than 2" narrower. That's about 1.8 sq ft greater frontal area for the Fit; a tenth or two in Cd would offset this (though I don't know what their relative Cd's are?). The Fit weighs about 140 pounds less (base models with manual shift), and it is ~10" shorter length.
So the Honda Fit is case in point.