It's not just seat angle. The BB height above the seat bottom also matters greatly for aero. It's about putting the body in-line as much as possible.
Many of the fast lowracers (NoCom, Morciglio) don't go far enough in either area, in my opinion.
My midracer had a 15degree seat angle with the BB 8.5" above the seat bottom. CdA (calculated by MyWindSock) was 0.18 at best. Not bad for a steel tube frame. And, no I don't have a problem with blood flow to my feet or making power in this position. I train in this position, so I'm fully adapted.
The new low racer is 12deg with the BB 10" above the seat bottom. First race is next Tuesday. We'll see how it goes.