318 MAX fuel economy builds?

The exhaust valve is the hottest part of the CC because it was just torched during the exhaust stroke. The charge will thermally ionize within that region. It makes the most sense to capitalize on that ionization by sending the initial spark kernel where it has the best chance of "getting lucky". Conversely, if the spark energy were sent to the intake side, the heavy ions in the exhaust region would tend to start their own combustion event once pressures got high. Can you say detonation??
You'll like this paper: