The methanol doesn't "come out in the heads" and batch size doesn't affect the final concentration as a % because roughly the same ratio is present during a run with a slight in crease in the tails due to the with methanol bonds with water.
Interestingly, after looking at this more closely, what I said is true of rakija, which is what I'm most familiar with (part of my family is Serbian), but appears to not be significantly true for grain distillates. Your sources mostly don't address these topics though; the latter one is mainly about copper and lead levels.