Solar Powered airplane

You've all by now seen the news articles. If not, look at

http://nexus404.com/Blog/2010/07/09/...fter-starting/

Its four engines, each about 10 HP, were spinning pretty big props,
the article says 3.5 meters. First question that comes to mind is, why
not a pusher configuration, that is marginally more efficient. Even
though the wings are thin relative to 3.5 meters, there would be
losses from the air cone impacting the wing, those losses would be
lessened since the inducted air is not as 'directed' and is of a
somewhat lower density.

The article mentioned it took off in the morning, and pretty much
flew circles all day and night. I wondered if there was an intention
to fly so that the solar panels were more nearly orthogonal to the
sun in the morning and evening, you'd gain power at pretty much the
cosine of the angle.

They did not tell us what the minimal sink rate of this beast was, but
it had to be pretty low. If it's as much as 300 feet a minute (I think
the weight was 3,500 pounds) that means one would need to deliver
about 30 horsepower to the air). That is not going to happen with only
40 shaft horsepower available.

I'd be really interested in someone with an aeronautical engineering
background offering some observations. The proof of performance flight
was successful, so the design as delivered worked, but I'm wondering
what other improvements would be obvious to the skilled observer.