You're taking some of this literally and it's not meant to be so.
If you look at a hologram it seems to have three dimensions, but when you see what it really is (light patterns interfering with itself) you can see that at the source, it is a two-dimensional object reflected in a three-dimensional medium. The astral plane has no physical dimensions- what you see in the astral plane is your projection- an entity can be 'flat' or even nondimensional- a point- but you will perceive it in a three dimensional way because that is what you're used to see- we interpret a signal or energy and give it form according to what we understand.
Like what many have said before- all negs are not the same or of the same nature- so this is why we have so many different types of countermeasures- to try to see which one works for what. A shotgun approach, but it's the best we.ve got.