The Living Force
This diagram is interesting and if I may point to the top right 6th density STS thought center. I do believe one can be “visited” contacted through thought energy waves. Don’t want them riding the wave to youMaybe this quote from the glossary may help you, beside a picture of the densities down below. I don't if I remember it correctly but STS has the tendency to get more "dense" and maybe cannot evolve until a certain threshold since of their material attitude and attachment, though I think your explanation does make sense.
From the wave chapter, the tree of life:
And most likely the part you remembered?