I'm 6'6" and weigh 230-235lbs. When I get to the top of a hill, people line up behind me like little ducks. Same thing on the flats as I punch a fairly big hole in the air.

There are a few things at work here, but in general terms, if you take a heavier object and get it going the same speed as a lighter object, the heavier object will go further because it has more momentum. So things like wind will have a bigger impact on the lighter object (throw a baseball as hard as you can and throw a similarly sized wad of paper the same way and see which one goes further).

Without getting into the fancy math of it, even at my extreme (for a cyclist) proportions, when I get tucked into the drops with my back flat, I'm not THAT much less inefficient than smaller dudes. So my considerable advantage in momentum more than outwieghs my relatively small areodynamic disadvantage.