User blog comment:FairyRaven/Fairy Tail Chapter 362: Natsu vs. Jackal, Review and Commentary/@comment-31.132.65.50-20131129140428/@comment-7418318-20131130085815

Lyon and Jura were both leaders at one point, while the other three were just side-kicks in all their appearances, so maybe that's how they "fell behind" despite appearing earlier.

That'd actually make Kagura more likely to be first, come to think of it.

But I see what you mean. I don't think Mashima goes by a fixed pattern, but rather just by how he feels.