Manifold heat cross over physics and benifits

I am interested in discussing it. I wonder if the heat cross-over was designed for worst-case conditions, like Alaska or Minnesota. Did the Mexican market get them? Not sure they even got cabin heaters there. In the 2 Mopar V-8 intakes I have pulled, the cross-overs were plugged solid with carbon, so no cross-overing was happening. I prefer mileage to power, so I try to keep mine flowing.