The quench absolutely changes with milling the head. Think of it this way. As you mill the head, you close the chamber a little more. Correct? As you close that chamber. You change the "roof" of the quench area. You move it in and towards the valves. This absolutely has an effect on quench, that's why you see dish pistons with quench bands. Yes. You can set the same quench HEIGHT with the appropriate gasket. But you've still changed the quench area.
