Pocket Universes

In Brandon's most recent [Livestream,](https://youtu.be/A67G4ObX7CM?t=2054) he said that if he got the power of a shard, he would create pocket universes. Then he shortly drifts off and said that pocket universes could only be created in the spiritual realm.

My understanding of the three realms is that, even though distances are not consistent, every point in the spiritual realm correlates to one point in the cognitive and physical realm. So would a pocket universe in the spiritual realm be completely disconnected from the other two realms?