I've heard the same. Yes, closer to the headers; the goal of the crossover is to reduce exhaust pressure wave overlap, or pressure buildup on either side of the engine. The crossover relieves this by channeling some of the pressure to the other side of the exhaust system. If I'm remembering right, the goal is the get the crossover as close to the source (cylinder heads/headers) as possible. There is a LOT of information available about exhaust gas sciences, and I bet if you look at HOT ROD Magazine's website, you can come up with something, they've done a few really good articles on it before.