I heard the 10:1 ratio a while ago, and for "Hollywood films". So I'm guessing on-film, but where film/processing budget isn't much of a limiting factor. Primer was released in 2004 so at that time most things would have been on film.
That said, I'm not in the industry, this is just what I've read about the production of Primer, so if your experience was of 2-3:1 that may be more accurate!
