I'm convinced that substrate plays a role in surface film.
I have 4 planted tanks: 2 with gravel, 2 with black eco-complete. Both tanks with eco-complete have a serious surface film problem. All of my tanks have anubias, java fern, and crypts. One tank that has a surface film problem has a cannister, the other has an overflow type filter (fluval spec tank).
I use a surface skimmer in conjunction with my cannister filter and it takes care of the surface film. I haven't worked out a solution for the 5 gallon spec. I've tried putting a piece of plastic along the overflow slots, creating a waterfall effect into the back filter portion but it doesn't really do anything.