I don't think anyone specifically knows. If you ask the physics, they will point to changes (like pulse shape or component sizes) they made due to their increased understanding of the physics. If you ask the target design people, they will point to decrease fill-tube size and number of defects in the capsule. If you ask the facility, they will say their ability increase both power and control power delivery. Likely, it is a combination of everything.

The other point that has been mentioned to me is when you in the self heating regime, there are exponential returns on increasing "quality" of a shot.