Just like you, I tend to believe that smaller empire suffers low number of anarchy. When your empire gets bigger, it will be longer. This is based on my experience so far. The best I had with non-religious civ is 2 turns when I had 4 cities in my empire. In a big empire, I usually won`t get any lower number of turns in anarchy than 5.
BTW, religious civs now has 2 turns of anarchy in C3C 1.15!