I haven't had time to do much ventilation lately, but I just completed knotting this small front partial piece. It is fully single strand/single knotted, and is cross-ventilated to add some lift. I used #16 Brazilian hair from YYhair.
The density is higher than I would normally like, but this piece was made to replace the hairline on an existing topper which is quite dense, so I tied the hair using one knot per hole, with slight graduation at the hairline.
The hair will finally be dyed to match and attached to the existing piece.