As you already know, Earth is locked as a prison and there is quite more to Earth before reaching the prison walls, so to say, than our incarnated plane.
Actually, as mentioned several times there are more Is-Bes (keeping with the same terminology) waiting to reincarnate here than incarnated and they are not just sitting in wait. There have been several depictions of cities in such planes, from dense planes full of darkness to better planes of all kinds and, most importantly, all within Earth's prison walls. I say most importantly because then it is easy to see that the stable cities of this kind would be of interest to use as outposts by extra-terrestrial groups interested in the human population here.
A notorious depiction has even been elevated into a movie production, the "Astral City: A Spiritual Journey (2010)" movie made based on the first book of a series.
Hence I propose a project to study these planes, their respective cities and their interaction with us incarnated humans and the extra-terrestrials.