User blog comment:Jopjopjop/Volume 19 Spoilers/@comment-16281343-20141220113254/@comment-16281343-20141220114117

Can go either way. There can be 100 or 100,000 Devils in that 1500 difference.

Though Rias said in Volume 2 that he became a candidate to have a title in the official game. So, imo, he's in the middle-to-upper middle.