John,
I meant to type "knotting" instead of "ventilation". Front hairline always has half-knotting, at least the units I have been getting. Hair in other areas has single-knotting. If I am unlucky, I get a piece with multi-strand knotting which is the worst with huge knots (even at 60% density). I once ordered a unit from a company in Washington state and that had 2, 3, or 4 strands in every knots. That was the worst.

Do you think half-knotted hair knots are easier to bleach? I am asking because knots in the front are almost invisible. I am wondering why half-knotting can't be used in the crown area. Is it because the way 2 strands of hair come out of knots? Maybe realistic crown can't be recreated with half-knotting?