You got the picture, Joe. Looking at a stovebolt head, most of the open area of the combustion chamber is on the spark plug side, so taking more metal off there makes sense. It also minimizes the distance the intake valve is moved toward the piston, so less material needs to be flycut from the piston crown for valve clearance. There doesn't seem to be an advantage from a valve angle difference on the 6-cylinders.
Jerry
