Charles: I disagree that you need a narrative as a prologue to what is happening in a fantasy or science fiction, unless you define the genres in such a way as, indeed, you have to have such a narration. You say that genres that don't need such an introduction aren't really outside of human experience. OK, fine, but then we begin to asked questions like--is it really fantasy or SF? I'm not sure what the point of that is, unless you're dealing with an editor who only publishes such things, and has a specific definition in mind ("Can't have robots. We already have robots. So it's not science fiction.") I think the best of the F/SF genre does take human experience and puts it in a new context. I feel a little defensive here, but I really don't care what my stories are called. Indeed, the first turns on jealousy, intrigue, and reactions to betrayal and coming down in the world. If that means it's not fantasy, that's fine. I deliberately limit the technology (with a few exceptions like anti-gravity) to which will most likely be achieved by the end of this century. Thus, "warp drive" isn't science fiction by your definition. The magic is limited to the Mabinogion, for the most part, but employes other tropes, like Gypsy curses. The gypsy in Stephen King's Thinner is similarly modelled: a curse to nakedness is parallel to a curse to thinness. Involuntary nudity is a kind of disability, which isn't beyond human experience. A fight for the throne, a civil war, and neo-colonial style imperialism isn't either.
I agree with Fred Miller's definition of science fiction vs. fantasy. SF is in an orderly universe, governed by understandable natural laws. Fantasy isn't. It is a squishier context, but a world where there is sorcery, one has to be careful not to run afoul of witches, mind manipulation, and one that has medieval knights, castles, and context surely counts. If not, then I'm content with calling it "adventure," "historical romance," or just WTF (which is why I contemplate self-publication). But I've read stories labeled "fantasy" by conventional publishers (like Tor) that take place in 1st person or limited 3rd person).
Star Trek wasn't a critical or popular success because the critics and the sponsoring network hadn't done proper democraphics. The year NBC canceled it, they did run such a demographic analysis, and although ST: TOS didn't have the 30% of the viewing audience they were looking for, the engineers, professionals, and college graduates who watched it bought an awful lot of really big ticket items. So they lost money when they canceled it. Kirk, to my memory, never explained what the Federation was, who Klingons were, or went iinto warp drive, teleportation beams that defied Heisenberg's Uncertainty Principle (hence, why TNG introduced the notion, again w/o explanation, of "Heisenberg Compensators" (they figured those engineers, et. al. would know the contest and why transporter beams are more magic than technology). Kirk just did things like say, "None of us realized that each was perceiving a different woman," which raised the question--how did he know it to put it in his log? It was clearly an artificial device, and grated. I think an introduction risks the same thing. Or an omniscient point of view that over-explains. Tolkein, in the Hobbit, takes it for granted a hobbit would live in a hole in the ground--albeit, as mentioned, a really nice one. No--"because of the economics of Middle Earth, the problem of scarcity was solved by a patronage system that put hobbits in holes in the ground."
Anyway, back to helping Akhere, I would advise him *not* to have a long introduction, to sprinkle explanations through the dialogue in a natural way. He wondered whether there should be rings around the planet, to clue the reader into it's not being our world. I told him one character could say, "ooh, the rings are beautiful tonight." (Substitute for 'the moon.') Heinlein, in Starship Troopers, had a Lt. Colonel run the Ethics class to point out some of the ways the world came into existence. No introduction. We're thrown into the middle of the Terran Army fighting an alien species. We don't even know, until a flashback, how the war happened. The Moon is a Harsh Mistress, another example. Double Star. Not as easy in fantasy, I concede, but the use of mythological traditions (like the Mabinogeon) help.
Or you can go the Gormenghast way, and have 100 pages of intro before anything happens.