Aerodynamics / Aerodynamic Cost / Aero parts

Are you suggesting that losing mass off the rider/decreasing the rider size might be the best thing to do?

It's a contributing factor, yes. Less body fat is less size and also allows you to get lower without legs hitting stomach.

But there's more to it than that. Flexibility, the ability to hold your neck out down and low, etc. Shrug your shoulders and your arms are closer in. Raise and lower saddle to flatten back or reduce shoulders exposed to air. There's lots of things you can alter about your position whatever your body shape.