The thing I like about next to is that it does not specify whether it is to the left or to the right.
However, for the vertical next to, it appears one needs to specify whether it is “above” or “below”. I find quite interesting why this would be the case (cf. various other vertical versus horizontal biases: reading direction, attentional acuity, etc), but I also find it quite annoying.
I would like to find a word that is the equivalent of next to but which applies to the vertical case. That is, it indicates that a position is either above or below, without specifying which of those two applies.
Sample Sentences, assuming the preposition is abaqine:
"The sparrow abaqine that falcon is casting a shadow on that sand dune."
"Look at those macaques, they're all climbing abaqine one another."
"In my fridge all the good food is abaqine each other, so I can't get it without toppling it all over."