I have divided double fans only once, and the results are what I expected. I planted them all together, but the fans acted like single fans, and aren't increasing like a double fan would, if it was still connected. So, I was sent 3 double fans two years ago, and I divided them, and I still have only 6 fans, even though they were planted close together. Pretty much every double fan that was planted at the same time has increased by at least one, but some by much more. That alone tells me that it is much better to not divide them if they are still together when you get them.
