A well-designed running asymmetric can rotate around and away from the blanket effect of the mainsail, which allows it to go low without collapsing. The Rotation is controlled by crew weight and the shape of the sail in conjunction. Get the boat to heel to weather and gravity helps rotate the sail.
This technique is really important for boats with bowsprit Asymmetrics who will not plane easily, and therefore must run pretty deep for the best VMG (like a J-109)
It is with this “positive” luff round that the dynamics of the sail pull the draft forward dramatically and as a result it rotates better, and as it does it puts the draft even more forward in the sail.