An article published in 2012 suggested that ranking between 10-11 programs would yield a >95% chance of matching.
I was advised when ranking programs that I didn't love as much, to ask myself if I would rather not match vs be an ophthalmologist at all. Reapplying to the match is tough and requires hard work in the time between applications. I would be inclined to rank every place I interviewed at unless it's not in good standing.