User blog comment:FairyRaven/Fairy Tail Chapter 375: The Supernatural, Review and Commentary/@comment-7418318-20140317103924

The only two 9DG we saw beaten so far, were far away from Cube where their book most likely kept. But the Demons within Cube are giving even Erza and Mira a hard time, not to mention Silver and Franmalth have so far been totally dominating Natsu (considering Franmalth's demonstrated power, just how freaking, scarily powerful must that make Silver, if Fran cowers before him like he did?).

Could it be that the Nine Demon Gates's power is diminished the farther they are away from their book?