things on the same plane as you get as smaller as they recede

Plane has nothing to do with it. Perspective occurs in all directions/dimensions. If something gets farther away from you, it will appear smaller... period, no exceptions whatsoever (under natural/normal circumstances - obviously magnification and such things can be used to counter/nullify that angular size difference)

THINGS WAY UP IN THE SKY DONT, BECAUSE U CANT PERCIEVE THEIR DEPTH

It is true that it is harder to gauge the relative size of something in the sky (without fixed reference to compare it to), but yes we can perceive the apparent size difference of things in the sky (such as planes) as they recede as well.

As for the sun, it too changes size as it changes distance to us and this is measurable - even if it is difficult for us to perceive with the naked eye. Plane has nothing to do with it. The rules of optics work the same no matter which direction/dimension you look, or how far away things are.

aIR DOESNT CAUSE REFRACTION,

As you said, any light traveling from one medium to another with a differing refraction index does refract! This includes air, which behaves as a fluid. Do you think refraction doesn’t happen in water too? Although gas and liquid are certainly different states of matter, they both act similarly - as fluids.

A DENSITY GRADIENT OVER DISTANCE = atmospheric DIFFRACTION

Not really, no. However there are physicists that agree with you that there is no significant difference between diffraction and refraction - they are one and the same. In my view diffraction is caused by light blocking/absorption/reflection and refraction is caused by altering the speed of the light wave. Refraction happens with frequencies of light where the medium (air) they are traveling through is largely transparent. Transparent things that cannot absorb/block/reflect light cannot diffract, but as i said - there are capable physicists and textbook authors that disagree with this view and declare that both are exactly the same. I think this is largely a semantical sinkhole. Wether we call the phenomenon of the light being curved convexly towards the ground as refraction or diffraction doesn’t change its reality at all.

are only ever perceived in 2d

That has to do with the distance to the object, its size, and the distance between our two eyes. It may appear 2D to us, but we can rest assured that like everything else in reality - it is, in fact, 3D. We don’t see it that way, but it is all the same. Do you disagree?

FAR UP. yOUR DEPTH PERCEPTION ENDS AT THE HORIZON

Sort of. I don’t exactly disagree, but the horizon (the distance limit of our vision through air) is NOT the same towards the horizon as it is towards the sky. The horizon is an optical illusion.

We can see farther than the distance to the horizon when looking through less air (i.e. looking up).

sO THE 3D FOREGROUD OCCULTS THE OPAQUE 2D BACKGROUND AT THE HORIZON, THIS IS WHY THE SUN APPEARSD TO SET.

i think this is word salad nonsense. The “2D” background is still plainly visible as the sun sets. There is no “occulting” by the 3D world closer, nor is such a thing possible. The sun can, and does, go far enough away that the amount of atmosphere between us and it is too great for the light to directly reach us anymore (we call it night) - and is “occulted” (I would say blocked) by it. However, if this were the cause of the sunset the sun would never set. It would remain the same size and fade until too dim to see. The bottom of it and/or ships would never disappear.

Again, can you demonstrate this believed principle/phenomena on a smaller scale? If not, why not? It should be easy to make an apparatus with smaller eyes (or use a small child) much closer together to test and observe this in a scale test if it existed - right?

iT SOUNDS LIKE YOU DIDNT WATCH THE VIDEO

I did watch the video, but am happy to admit that i may well have not understood it.

Let’s assume you are correct - how can we observe this occulting phenomenon in a controlled repeatable way? I can demonstrate a mockup of my explanation, and although that does not mean that is for certain what is happening in reality - it is at least conceivable and demonstrable. It sounds like your explanation may not be demonstrable/testable, which makes it far less likely as a possibility.

things on the same plane as you get as smaller as they recede

Plane has nothing to do with it. Perspective occurs in all directions/dimensions. If something gets farther away from you, it will appear smaller... period, no exceptions whatsoever (under natural/normal circumstances - obviously magnification and such things can be used to counter/nullify that angular size difference)

THINGS WAY UP IN THE SKY DONT, BECAUSE U CANT PERCIEVE THEIR DEPTH

It is true that it is harder to gauge the relative size of something in the sky (without fixed reference to compare it to), but yes we can perceive the apparent size difference of things in the sky (such as planes) as they recede as well.

As for the sun, it too changes size as it changes distance to us and this is measurable - even if it is difficult for us to perceive with the naked eye. Plane has nothing to do with it. The rules of optics work the same no matter which direction/dimension you look, or how far away things are.

aIR DOESNT CAUSE REFRACTION,

As you said, any light traveling from one medium to another with a differing refraction index does refract! This includes air, which behaves as a fluid. Do you think refraction doesn’t happen in water too? Although gas and liquid are certainly different states of matter, they both act similarly - as fluids.

A DENSITY GRADIENT OVER DISTANCE = atmospheric DIFFRACTION

Not really, no. However there are physicists that agree with you that there is no significant difference between diffraction and refraction - they are one and the same. In my view diffraction is caused by light blocking/absorption/reflection and refraction is caused by altering the speed of the light wave. Refraction happens with frequencies of light where the medium (air) they are traveling through is largely transparent. Transparent things that cannot absorb/block/reflect light cannot diffract, but as i said - there are capable physicists and textbook authors that disagree with this view and declare that both are exactly the same. I think this is largely a semantical sinkhole. Wether we call the phenomenon of the light being curved convexly towards the ground as refraction or diffraction doesn’t change its reality at all.

are only ever perceived in 2d

That has to do with the distance to the object, its size, and the distance between our two eyes. It may appear 2D to us, but we can rest assured that like everything else in reality - it is, in fact, 3D. We don’t see it that way, but it is all the same. Do you disagree?

FAR UP. yOUR DEPTH PERCEPTION ENDS AT THE HORIZON

Sort of. I don’t exactly disagree, but the horizon (the distance limit of our vision through air) is NOT the same towards the horizon as it is towards the sky. The horizon is an optical illusion.

We can see farther than the distance to the horizon when looking through less air (i.e. looking up).

sO THE 3D FOREGROUD OCCULTS THE OPAQUE 2D BACKGROUND AT THE HORIZON, THIS IS WHY THE SUN APPEARSD TO SET.

i think this is word salad nonsense. The “2D” background is still plainly visible as the sun sets. There is no “occulting” by the 3D world closer, nor is such a thing possible. The sun can, and does, go far enough away that the amount of atmosphere between us and it is too great for the light to directly reach us anymore (we call it night) - and is “occulted” (I would say blocked) by it. However, if this were the cause of the sunset the sun would never set. It would remain the same size and fade until too dim to see. The bottom of it and/or ships would never disappear.

Again, can you demonstrate this believed principle/phenomena on a smaller scale? If not, why not? It should be easy to make an apparatus with smaller eyes (or use a small child) much closer together to test and observe this in a scale test if it existed - right?

iT SOUNDS LIKE YOU DIDNT WATCH THE VIDEO

I dd watch the video, but am happy to admit that i may well have not understood it.

Let’s assume you are correct - how can we observe this occulting phenomenon in a controlled repeatable way? I can demonstrate a mockup of my explanation, and although that does not mean that is for certain what is happening in reality - it is at least conceivable and demonstrable. It sounds like your explanation may not be demonstrable/testable, which makes it far less likely as a possibility.