In term of pure drag, you're right, you want to reduce the surface and that's not what this design does.

However, for aerodynamic efficiency it is the lift/drag ratio that matters. And while in a normal airliner the body provides very minimal lift, here it's basically a wing and thus generates a lot of lift.

The end result is that while the drag is probably worse, lift is likely improved enough to compensate.

(Also, drag might not be that bad given you do not have a tail, which is pretty awful aerodynamically speaking)