PR does have a point. Most FJ aircraft just have convergent nozzles meaning much of the expansion energy is wasted outside the engine. It would be most efficient to have a large convergent-divergent nozzle (like the main engine nozzles on the back of the shuttle) which would capture the thrust generated by the full expansion of the exhaust gases behind the aircraft. However, the drag and weight would be excessive when not in reheat (90%+ of the time). Latest generation FJ engines have (variable) con-di nozzles but even then, the limited diameter means that they still can't recover all of the expansion energy.
N Joe