You would need to measure it yourself, but I believe that they are the same dimensions as a 22/3000 tank, just not as long. In which case, they do fall under the 2x2 rule. Granted, some manufacturers still recommend getting them hydrotested.
As far as I know, all of the companies, like GA and Ninja, that put out a 13/3000 tank use the same tank manufacturer. So they all have the same dimensions. Of course, there are a few other sizes, like 8/3000, 22/3000, and one other that I can't think of right now.