Thank you for your quick reply, but .... as per AFCAD actually the stock airport is at 12.999 ft whilst yours is at 13.297 ft (version 1.04) but that alone cannot be the difference
That's not an issue, at all. The difference you are seeing, which is normal and it's expected, it's the 4 meters difference between ground a 13.0 ft (4.0 meters) and water at 0. As I've said, it's normal and you are supposed to see that.
Fact the scenery was intentionally made like this, should be apparent from the little pier, which matches exactly the altitude difference between the shore and the water.
Also concerning mesh, I read your hires mesh is 4.75 so is Nextmap for the whole island.
In this case, our mesh would probably show up anyway, because at the same resolution, the one on an higher layer should prevail. However, our mesh only usage is just to flatten the airport against *other* meshes which usually have bumps in the airport area which sometimes pops through the runway/taxiways.
When in FSX water seems to be at 6.0 to 6.9 ft (depending on the waves) whilst the airport is at 22.1 ft in your scenery.
No, it's not. The airport it's at 13.0 ft as per the AFACD. However, if you are reading the altitude in slew mode, the plane wheels+eyepoint height from ground is added to the readout so there will be a difference in the readout, but the airport is at 13ft from ground
These unrealistic high cliffs are a pity but obviously wanted by the designer...
They are not unrealistic high, they are at the correct height as published.
The real issue is that FSX doesn't really support sloped surfaces, because that disrupts the AI flow over the taxiways, which includes also ground vehicles, so the airport has to be flat, and the only possible altitude to flat it to, can't be anything else than the airport published reference altitude. In real world, that part of the airport would probably be at a smaller altitude, maybe 5-6 feets instead of 13.
We might *try* to ease the transition on the cliff to make it less abrupt, but it will not ever be like in real world, for the reasons mentioned above.