Bacchetta Aero Body Position Ideal 
by Rich Pinto (of Bacchetta Bicycles)  

The Aero seat angle that is the best compromise between aero and hill
climbing for most people is 25-30 degrees, in my opinion.  This would be measured from the side edges of the seat, with a straight edge spanning the lumbar curve.

If an Aero's seat angle is in this range it will allow most of the
spinning leg and foot circle to stay almost completely inside the reclined
torso's shadow. 

Further decreases in seat angle will cause large parts of the
spinning leg circle to penetrate the torso shadow. Also, the torso/thigh
angle will increase, and most riders will feel a decrease in hill climbing
and maximal power.  The rider’s view of the road in front of the bike can also
be increasingly compromised.

My ideal is to get behind a rider (from a distance of 30 feet or
more) and see nothing but a fairly reclined torso and the back of the
shoulders above the seat.