Spaceborne bases may not hide. Their positional stabilizers cause a bunching of spacetime that can be seen easily. Even those in orbit of planets cause this. The exception is System Activity Maintenance Stations (SAMSs) in empty sectors. They may use the HardToSee attribute in the script.
Any base smaller than a Starbase/YDK in a nebula may use the HardToSee attribute (ground and space). Any base smaller than a BATS in an asteroid field may use the HardToSee attribute (ground and space).