Thom this is a quote from the developer about the system order before 6th Jan, I dont think it will help you though, " Before it was random (at the database server's discretion)."

~Tour

Well... I had three chances to figure it out...

I believe it was based on how close you were to the level just before leveling. For Cat... I got very close to the level, within about 4000 exp, then I went after the tax-collector... the highest exp monster I could see. That put him on top.

For Pelo, I planned the same, got him within 3000 to the level, but I messed up and dug... that put me over by only a few thousand experience. But Pelo went above Cat. 

I got arti even closer to about 2000 below level 100 and then finished on a random monster.

So either my explanation is correct, or rank is based inversely on clicks. But I doubt that. Click order holds for the first several, but it doesn't hold all the way down.

If I really cared... I would have slotted Arti between Pelo and Cat... but I wanted to maintain the fiction of exp/click.