Yes, like I said though, there are a number of variables involved. Hip angle is a big one too.

Now, thanks to the arthritis in my back and neck, I just can't do the whole "get low, get aero" thing like you see a lot of people doing out there in triathlon. My position, so far as my back is concerned, is really not a whole lot different than my position on a road bike down in the drops. But I'm noticeably faster on a TT bike, even with a relatively similar position. I think there are two factors that account for that. First and most important, is hip angle. TT bikes do tend to have steeper seat tubes, plus I have my seat cranked absolutely as far forward as I can get it. This helps open up my hip angle a little bit for better breathing and better leverage on the pedals. Second is I just presenting a smaller frontal area to the wind. Yes, I have aero bars on my road bikes, but I'm higher on them because of the built in geometry of a road bike. I can get lower out on the drops, but that opens me up more and presents a larger frontal area.

So it's a balancing act. I've been passed more times than I can count by people chugging along on a road bike. They have it set up well for them. Me, I'm not nearly as comfortable on any of my road bikes as I am on my TT bikes. They just fit me better.