You'd think A refraction index with that kind of power would show a SUN or Moonrise shifting into view from the 'convex curve optical illusion' point (whereever that may be on the flat horizon)

I’m not sure i am following you. We do see the moon/sun/boat/distant object appearing to rise out (“shifting into view”) of the horizon line as it approaches us (and vice versa).

you can watch them appear/disappear over the horizon even with a telescopic lens

True. Zooming in on the optical illusion doesn’t change it. Why do you think it would?

In your view , it's the density gradient that shifts them out of view right at the 3 mile horizon point 6ft above see level.

More or less, yes - exactly. Well, more correctly in the case of the sun, moon, stars, planes, etc (anything not on the surface of the water) - it appears that that is the case! The horizon line is distinct/separate from the density gradient that causes the light from the distant objects to curve convexly towards the surface. The light from the boat curves enough to appear to sink, at that 3-7 (approx) mile limit.

Please let me know if you have any other questions and/or criticisms!

You'd think A refraction index with that kind of power would show a SUN or Moonrise shifting into view from the 'convex curve optical illusion' point (whereever that may be on the flat horizon)

I’m not sure i am following you. We do see the moon/sun/boat/distant object appearing to rise out (“shifting into view”) of the horizon line as it approaches us (and vice versa).

you can watch them appear/disappear over the horizon even with a telescopic lens

True. Zooming in on the optical illusion doesn’t change it. Why do you think it would?

In your view , it's the density gradient that shifts them out of view right at the 3 mile horizon point 6ft above see level.

More or less, yes - exactly.

Please let me know if you have any other questions and/or criticisms!