Mental space and its existence is what makes things like remote viewing possible. There shouldn't be any limit to it. As I understand mental space, one of the differences between it and physical space, is that there is no space in it. All the distances are associative. In the real world, Land's End and John O'Groats are famously far apart. Yet you can't say one without thinking of the other. In conceptual space they are right next to one another. Distances can only be associative, even vast interstellar distances shouldn't be a problem. Time would also function like this.

De Abaitua interview (1998)