If this seems indeterminate then that's because fiction includes the things we've been discussing:
- jungle action
- amazing fantasy
- tales of the unexpected (I wonder if you get a refund if the tales are not as unexpected as expected)
- weird western tales
- good old superheroes.
It also includes genres not identified with the medium, such as murder mystery and spy thriller.
I may also have confused matters by applying the same yardstick for measuring what is fantasy and what is fiction i.e. a location in time preceding the advent of heavier-than-air craft taking flight. Any depiction of such in a story published then would necessarily be both. But consider two fisted tales, where the objective (in addition to being entertaining and captivating) is to show the raw blood and guts brutality of the battlefront - any element of fantasy, such as a haunted tank, would run counter to that purpose. But they could still be fiction.