I will not argue with your success, but it is generally considered disadvantageous to bring the boom above the fore-'n'-aft centerline of the boat (normally it is not even brought all the way to to the centerline).
This is because you will end up with quite a bit of hook in the sail, such that some of the breeze may be hitting the sail for the first time on the windward side near the trailing edges. This is bad for the "flow", since you want wind to pass over the leading edge and retain a laminar flow along both sides of the sail, then exit smoothly along the leech for maximum aerodynamic efficiency.
I would suggest you get some empirical readings via gps to see if the advantage you perceived was real or wishful. You may have gained an advantage, but it may have been for other reasons (such as the slot was too tight between the mainsail and the genoa, and over trimming the main with the traveller reduced some of that drag...)