And the whole issue of perspective eludes your mental grasp.
Yes. I remember one time I couldn't work out why a frisbee I could see kept getting bigger.
Then it hit me...
On any certain day of observation, I can watch a jet pass overhead, exceeding the ceilings of the clouds. As that jet passes further down range, the cloud (which the jet obviously passed over the top of just seconds prior) now appears lower in the sky to me than does the cloud, yet the jet made no change to altitude.
Yes. I literally showed how that could work with the photo of the row of lamp posts above.
But "perspective" was Tom's answer to how SHADOWS can be cast upwards. I have explained above, with proof, how that is impossible.
In your scenario if someone on the plane was to shine a light on the clouds which is powerful enough that the cloud casts a shadow then even though FROM MY PERSPECTIVE the jet appears below the cloud it is still PHYSICALLY above the cloud and so the shadow would be angled downwards. That is how shadows work. If you don't understand that then I'd suggest it is not my mental grasp which is being eluded.
I doubt any man-made light would be powerful enough to cast a light on any natural surface found on Earth, but the point still remains regarding why the Sun (obviously higher than the jet, larger than the jet) can still appear "lower than the clouds<" and still account for being able to "illuminate and cast shadows," under the clouds.
Reflection is a better answer but the ground would have to be pretty much be mirror-like to produce that amount of brightness and cast shadows like in that photo so it's implausible.
Implausible? I do not think so.
If you have ever been subject to the Sun's reflected rays off of water or snow, not only can you be permanently blinded by these reflected rays (just as you would by direct exposure), you can suffer severe burns just as you would by direct exposure, with no change in severity.
While we're here, perspective also cannot explain the photo above which only shows part of the disc of the sun. If the sun is 3,000 miles above the plane of the earth then it cannot be seen to slowly disappear below the horizon as it does every single day.
That is a common misconception and, unfortunately, the answer lies in the way you choose to word things.
You claim below, I choose the word beyond.
I am not under some delusion I can see all things above my head at all times. Sometimes they still remain above the flat plane but are beyond my visual acuity for any number of reasons.