This is essentially true of mystery as well, since like much of SF mystery relies on hidden information being disclosed or discovered prior to the end of the narrative. It's more troublesome in the higher ends of fantasy, where the reveal is a lot less essential to the success of the story. On the other hand, high fantasy short fiction doesn't seem to be as common as contemporary fantasy short fiction or SF short fiction. Romance, where (at least classically speaking) the endings are comfortable inevitable, uses a different dynamic altogether.
When one switches to novels, or even novellas, I think this changes as well, simply because the sharp gain in complexity of the plot and the narrative as a whole.
Bonus question: Why do we link high fantasy and contemporary fantasy in our labelling?