Okay, so I have an island where the story will be based in and around. It's actually more of an atoll, similar to Bikini or Kwajalein in the Marshalls, with the island parts being in somewhat of a ring around a deep-ish lagoon (bay?), but with more substance. I was mainly thinking of the caldera of an extinct volcano.
As you can see, it's basically a ring of mountains and jungle sticking up out of the ocean. As it's currently drawn, the island is only about 2.5 miles (4.6ish km) across, lagoon and all.
The Main issue I'm having is scale. I'd like to keep the atoll on the small side, but I'd really like for the ring of mountains to be able to totally block low altitude aircraft (no oxygen required, so under 15000ft/4500m). Sadly I can't reasonably convince myself that a half kilometer wide strip of land could support that and still have room for the story I'm planning. So I'd like something in the 8-10k range. I could settle for smaller mountains and just toss a "reason" in as to why the locals couldn't get over it, but I'm already flipping physics the bird with their airships, so I'd like to avoid that.
In case it matters: The atoll is near the equator of the planet in question, which is mostly earth-like (only real exception to physics when it comes to geography, but not on this atoll). The locals use fantasy-style airships, but haven't figured out the oxygen/altitude thing yet. And a lot of the story will take place in and around the brownish "Arrival Clearing" so that has to stay at a decent size.
So, the question: What's a reasonable footprint for a 8,000-10,000ft (2400-3000ish m) mountain, and how much would this design need to be scaled in order to plausibly ring the atoll?
Thanks in advance!