I think that sort of geometry would encourage the air to flow around the engine, reducing pressure & density of the air actually propelling the aircraft. This w

I think that sort of geometry would encourage the air to flow around the engine, reducing pressure & density of the air actually propelling the aircraft. This would seriously impact the efficiency of the engines, and I suspect this is what the article is referring to. A flat grille would be crazy as it would just collect the birds, held in place by the extreme pressure conditions.