This cover is known to be stronger, and because of this I use it with several plays. And such strength you cannot overcome, because two arms can oppose one very well.
Rather than giving an individual technique as such, the 6th scholar gives an alternative method of making the master cover. While the master cover typically uses a hooking block with a single hand, here you brace your left hand with your right to make a high posta tutta porta di ferro dopia.
As Fiore points out, the advantage of bracing your arm like this is to add strength to your cover. The most likely reason to use it is against an opponent who is physically much larger or stronger than yourself.
The left hand moves in the same way as the 1st master, but you use your right hand to brace the wrist. Although the picture shows the left elbow held high, this is mechanically weak. In practice you do not want to lift it any higher than usual. Having made the cover, let your right hand drop away and transition to any of the plays of the 1st master.