Quote Originally Posted by Debihuman View Post
Actually the Template applies to Any creature (there is no size restriction). According to the Pathfinder Swarm Template, any base creature from Tiny to Small uses +8 as its modifier. If you are using the swarm subtype but without the template, the modifier for those creatures seems to be the same the same as the base creature. Having conflicting sources does make things more difficult to assess.

The swarm template does not have a minimum size, but it was clearly designed with larger creatures in mind. I would direct you to reread the size and type section of the template, where it indicates the size change. The increased size bonus is because it's new size would be fine. And since the hypothetical diminutive base creature should not be shrinking in this context, they would stay diminutive, and use diminutive's size modifier.