I think that when 4Dsts go to 5D contemplation zone there are distince 'energy barriers' to protect the harmony of 5D. Also because entities are attracted to those of similar energies - affinities, even for STS, they are 'guided' to the 'lower realms/spheres' of 5D. The umbral/hellish places that their intentions/choices/actions fit them for.
At any time they can ask for help or 'repent' etc to rise to the the next sphere.
However, their lies and manipulations are evident in the 'energy' so they truly have to be genuine if they ask for forgiveness as all thoughts are transparent.
Those who have 'relatives' in such areas are permitted to 'visit' though only as part of a team,for their safety, should they wish to help 'encourage' them psychologically. Though I don't think it is quite as straight-forward 'encouragement' as we view it due to free will.
There are regular 'charitable' teams that visit lower areas to do all sorts of work - to our planet too - consistently.
There is much para 'technology' used for many different instances including 'buses' that are used like 'shuttles' to our world (though these could be purely psychological crutches for the recently departed who wish to visit their living families). As we also know that travel is purely by volition - thoughts/intention.
There is also the possibility that cities are created directly above the relevant city here on earth. This may well be done by those who have the persistent craving for the 'life/homes' they left behind. In fact it occurred to me that should that 'city' filmed in the sky in China not have been a fake, it would exactly represent what such mentally created cities would look like - nearly an exact replica.
Regarding how far from the ground 5th density is I recall two different descriptions. Firstly that the 'higher spheres' are approximately 7 miles above our planet. (This either from the Spirits Book, or Genesis).
Secondly, that T.C. Lethbridge in The Power of the Pendulum states:
"If I have thought this out right, the so-called Heaven of religious beliefs is another zone of living less than the height of an ordinary room above our heads, or perhaps twice as high. We cannot see it because all of its vibrations, whether of light or sound, colour, or any other kind, are too fast to register in our earth brains. Since the construction of earthly objects is in reality almost empty space, there is no difficulty for parts of one zone to pass invisibly through the other; although apparently everything on the third level will seem as real and solid to people living on that level as things do on this earth level. Earth then appears to consist of concentric zones of living all quite close together. Presumably you could destroy the whole present earth's skin with everything on it without making any difference to the one above, unless it was shocked surprise at such a stupid action.
Whether these zones, or onion skins, go on out into space to infinity there is no means of telling without using a pendulum of too great length to be convenient; but there is certainly a fourth ABOVE the third. The probability is that mind is undestructible, time limitless and the skins innumerable"
I do wonder though about serious nuclear blasts here affecting other spheres or levels, as other realities seem to interpenetrate or be interspersed. Even if they are non-material. Perhaps why the C's mentioned in the negative about nuclear (if I am recalling correctly?).