User blog comment:Ryuzakiforever/When Will FUNimation Catch Up?/@comment-4374114-20150203150627/@comment-34981281-20150203161648

I originally worked the numbers at 13, but found that at 12, they cut off evenly at the end of each season. Therefore, it's completely reasonable to assume it will remain 12 each Voyage. The only one I can't be sure of is Dressrosa, which is sure to break Season 2's record.

As for the gap average, you're absolutely right, and being 4-5 years behind Japan makes more sense than 6-7.