Why is it not possible? It happens all the time on the Plane Earth.
You have yet to prove a curved surface projects a horizontal mirage.
In the RE superior mirage light bends down. That allows light to go over the curvature and reach the observer. Without curvature, light bending down would hit the ground or the surface of the sea, maybe the fish would see it, but not an observer sitting at same or higher altitude.
So how does the superior mirage work in FE? Could you please describe how is light bending and what is causing it, a diagram would help.
You also don't explain why the refraction makes the surface rise up and not the ship or the buildings or how can a mirage completely block the sight of the ships or buildings, what's stopping the light from coming through? And how can that possibly work consistently for every situation and for all observers looking from different altitudes and for every weather situation.
It just doesn't make any sense. What you are saying doesn't look possible and it doesn't even match what others FE say, I think you have misunderstood something. This is what others FE say, maybe you need to do some more research: