ok, I get what you mean, you get a undercut pocket at the back end, the fish can't go down or back, only forwards and hauling in the wings prevents this too. the only chance the fish have is going down through the space between the closing wings.
A lampara net is not a purse seine, as it has no rings or purse lines to close the bottom. Instead, lampara nets and purse seines are types of round haul nets of which there are hundreds worldwide. The small net pictured in the video would normally be kept as circular as possible during haul back operation, and hauling would stop at the beginning of the sack containing the fish and the net would be dried up by hand at that point. The construction of the two nets are radically different.
