I agree with what you say about having your weight muscularly supposed when in the drops.

But, I'm having trouble wrapping my brain around the hands in the drops being lower than elbows in clip ons. I'm 6ft and the distance from the crease in my elbow to the center my palms is 13in, or roughly 33cm. Drop 5 cm for bent elbows, and that leaves 28cm. Using a deep drop of 15cm, that means that the elbow cups of the clip ons would have to be 13cm above the tops.

Perhaps I've missed something?

http://www.bikeradar.com/...-aero-is-aero-19273/

This seems relevant to this discussion...

With a proper road bike fit you can comfortably ride the drops with your elbows bent to 90*. This makes you significantly lower. It also makes it possible to brake and shift in the drops. Resting your hands on the drops with your elbows straight is not the same.

Assuming you have bent arms on the drops it is very possible that you can get your back lower using the drops than on clip-ons given the same bar height (i.e., assuming the hoods remain in the same position for both cases).
However the section in bold above makes one huge and, I believe invalid, assumption: You are assumping that back height/angle is the defining factor in aerodynamics and even state that it's this "simple". It's not.

Width is potentially just as important or more important than height. It will depend on the shape of the individual, the choice of positions, the clothing, the speed, etc, but it's absolutely feasible for a higher narrower position to be faster than a lower wider one.
I have broad shoulders, they are still broad on the extensions but there is a significant difference. The extensions also bring my entire arms within a much smaller volume. I'm absolutely certain that I can raise my back a little, pull my elbows in and go faster.
Why do you think Cancellara and others use that forearms draped over the tops position? They would be as low in the position mentioned in previous posts where you grasp the top of the brakes and hold your forearm horizontal but the draped position also narrows the shoulders and brings in the arms like an extension and thus reduces drag.

I don't know how BBS numbers but I got a Retul fit on a fit stand (not sure what the proper term is) and at the time I couldn't afford a TT bike. What I could afford was a FF seatpost and a new stem with some clip-on aerobars. So we took all that and got me as close to the ideal TT position we could on my road bike. It came in pretty close actually.

I had some pretty good bike splits on that setup and no way in heyill I would have hit those marks on a traditional road setup.

Now if you just throw aerobars on a road bike and don't adjust anything else, then yeah maybe faster in true road position.

 
There are some stage races that won't allow you to use a TT bike for the TT. Some BS about being fair to people who don't want to drive to the race and don't want to fly with two bikes. In those cases it is possible to get decently aero on the road bike by using the drops, but the TT is typically less than 20 miles, even less than 15 sometimes. The position is doable for that length of time, not something I would want to do for 112 miles.

in which case, the invisible aero bar is the way to go. and those stage race ITTs are often less than 25 min in duration, which makes the IAB sustainable for that duration.

Elbows should't be straight with a good fit... At any rate, I just got on my roadie on the trainer. Couldn't make my wrists bend enough to allow 90* elbows in the drops. So I moved hands to the hooks. With 90*, my chin was on the stem. This doesn't seem like a "proper" fit to me. Perhaps I'm not understanding what you're trying to tell me. What's the drop from your saddle to bars in this "proper" fit? Can you post a pic of this more aerodynamic position from the side?

Thanks!

Nope all it makes is your elbows bent at 90 degrees. It only makes you significantly lower if the bars are significantly low.

I'm guessing that "drops position" means something like these:





and that "recreational aerobars" something like this: