Yes, upper wing has less angle of attack, makes no difference as to the sweep of the wing. You will find, due to the way the wind flows through the wings on a bipe, that the lower wing will not stall first. If you can, design the wing attachment so that you can experiment a bit. I tried many different arrangements on at least 12 different bipes, 7 of them being Aeromasters, and on all, they flew best with the upper wing at a lower angle of attack than the lower wing. Now, you could get them to fly with different arrangements but performance suffered. Now, if you only want efficiency at level flight and are willing to sacrifice maneuverability, then you can have the upper wing at a higher angle of attack and still trim for stable flight. When I did have such arrangement, I found that trim for level flight was much more difficult or critical with the plane having a tendency to gallop; i.e. pitch up and down during level flight like driving on a bumpy road.