What does “too close” mean?
Great question.
If there are multiple universes, then they would only exist as separate universe if they were separated from each other. Each universe would contain space, time, matter, and energy.
The void between the universes, in order not to be a universe itself, would have to be devoid of space, time, matter and energy.
This would suggest that there is no void, just a bunch of universes banging up against each other with infinitesimally small yet unimaginably strong walls separating them. Or it would mean that the universes are completely orthogonal to one another in completely different dimensions such that there is no imaginable way to move from one to the other.
The idea that multiverses are "too far" or "too close" to one another seems like a non sequitur.
When they rake their leaves, they all blow over onto our side.