The part of the Ethereal Plane that is beyond the Material Plane is the Deep Ethereal, here seen as the color red. The part of the Ethereal that overlaps the Material is the Shallow Ethereal, here seen as green. The Shallow is how one can walk thru the Material Plane ethereally. One can see the Material Plane from here, with minimal distortion.
Moving from the Shallow to the Deep, perceives the Material Plane distorting increasingly, until disconnecting fully from the Material Plane.
It seems to me.
The Feywild is the upper part of the ether, toward Positivity, and the Shadowfell is the lower part of the ether toward Negativity.
There is a neutral belt across the ether that is neither Positive Feywild nor Negative Shadowfell. This green part of this belt is the Shallow Ethereal. On the left and right, each side of this belt is the Deep Ethereal in red. This neutral belt is the Ethereal proper, while the Fey and Shadow aspects of the Ethereal are usually referred to by name.
Of course, this map with an "up" and a "down" is a model to represent different "frequencies" sotospeak of the ether, from high-energy Positivity downward toward low-energy Negativity, respectively. Actually, in the Material Plane, all of these planar frequencies coexist in the same place simultaneously.
To move from Feywild to Shadowfell is more like a Planeshift to shift frequencies. Planar travel isnt like teleportation to relocate somewhere else. The planar traveler stays in the same place but their own nature transfigures into a different kind being. To become fully ethereal, means to become made out of pure force, similar to the other spirits in the ethereal.
Likewise, to "enter" the Astral Plane means to allow ones own Material body of flesh and blood to remain behind − or to vanish − and to instead gain an angelic body made out of pure thought. This astral body is sometimes called a virtual body. Compare the Astral Projection spell that leaves the Material body behind while traveling outofbody as a thought construct. When a flesh-and-blood body vanishes it remains as an ethereal potential, so one can reconstitute it later when returning to the Material body. Switching back and forth between matter and aster, is like swapping bodies, back and forth, human and angelic.
Planar travel is unlike teleportation.
Most of the Shadowfell is in the Deep Ethereal in the red, but there is also a Shallow Shadowfell that partially overlaps the lower area of the green Material Plane. So it is possible for ghosts from the Shadowfell to coexist ethereally among creatures in the Material Realm. This is what makes shadow-walking thru Material Places possible. In the Shallow there is minimal distortion. There is an overlay of death and decay, but the Material places are accurately recognizable. There are also parts of the Shadowfell that are Deep, distorting until eventually disconnecting from the Material Plane.
Oppositely.
Most of the Feywild is the Deep Ethereal in the red, but there is also a Shallow Feywild that partially overlaps the upper area of the green Material Plane. So it is possible for fey spirits from the Feywild to coexist ethereally among creatures in the Material Realm.
The Shallow Feywild that closely overlaps the Material Plane and sees it with minimal distortion. A rock formation in the Material Plane looks the same in the Shallow tho slightly more vibrant. This Material overlap is where most of the Primal nature beings are active, including the minds of stones, rivers, trees, beasts, and humanoids as features of nature. Some humanoids are sensitive to nature beings and can reach into this Shallow Feywild from the Material.
As one planeshifts deeper into the Feywild, the perception of the Material Plane becomes increasingly distorted. Mountains become taller, distances between locations warp, the flow of time can change, colors become more lush and brilliant, contrasts more dramatic, and the healing Positive influence profuses all life, more and more, until finally the Deep Feywild disconnects from Material Plane altogether. Most of the Fey creatures, such as Dryads and Satyrs, are active near the border between the Deep and the Shallow.
In sum. The Shallow Etheral overlaps the Material Plane plus a Deep Ether beyond it. The Feywild is the Positive Ethereal. The Shadowfell is the Negative Ethereal.