Is there a difference between the 4 Divisions in NCPAL for 4th grade?

I was under the impression that the Board encouraged balanced teams through 4th grade (whether towns comply with that mandate is another discussion and based on the comments in this thread it appears that many towns do not). That said, if every town is supposed to have 'balanced' teams, are the Divisions merely structured to group towns that have similar abilities based on history?

Would be interested to hear if anyone can shed some light on how the 4th grade Divisions are determined.