ok,here is were i explain things,like always:
even when adolla apparently merged with reality, it doesn't mean that adolla is 3 dimensional or much less.
it is still a higher dimension or a dimension difficult to access.
you remember the portal?well,then you will remember that is stated that the portal does not exist,but also,for shinra and sho to enter,
they need to break into a particle level.
and when entering adolla,they are shown to be in a plane
were all is real,
they travel to the past.
the history of humanity despair.
and after traveling to the past,they manage to get to the adolla.
Which means that the only way someone can even get to adolla is by traveling back in time while in contact with the portal.
because in other times,they cannot enter physically to adolla(because is a higher dimension)they have to literraly have a mental connection to adolla.
this is show multiple times,but,for example,shinra was
sleeping until he enter to adolla,
and he meet sho in the adolla,
while the real sho,was in his throne(and even the narrator stated that shinra was able to enter while dreaming)
and also,you will ask,why they don't simply have the connection?remember,adolla merege with reality,and peoples ideas/perceptions and concepts are now a reality.
so to enter adolla, you have to forcefully do it through something mental, which would make adolla something that doesn't exist on the physical plane, for obvious reasons.
that's why the adolla is 3.5 or something does not make sense(in all the levels)because adolla does not exist in a physical world(3 dimensions)is exist beyond the past even.