Thats the way the AV8R was designed. No different really that planes like the Kingcat and REaction 54 that have their underslung turbines angled down. Since the AV8R has the turbine on top the exhaust is angled up to prevent pitch changes during changes in throttle. Looks weird but it works, as once the plane is trimmed for level flihgt it stays that way at all settings of throttle.

AJC