Another way to mitigate other-spacial contacts is to drastically reduce the amount of opposing threats you can meet. For instance, making sure that NPR count is at most 1.
There's also a setting that makes other empires either automatically succeed (without calculation) or automatically fail sensor contacts when they're in systems that the player has no presence in. The former option is so that enemies conduct warfare per normal, but they get it over with, skipping sensor envelope detection turns and going straight for the kill.
The other option skips sensor contact entirely, which should basically stop detection from occurring in systems that the player cannot witness anything. This means that you can have many threats in the galaxy without being bogged down by constant unseen wars. However, if you go several decades before entering a particular system, you might find that several alien races have made it their home, will rapidly tank their mutual standing due to the co-presence of military vessels suddenly being detected, and a massive galactic knife-fight of a war breaking out. This has some very interesting AAR report potential due to the sheer amount of military action being carried out by third parties, with the player only able to bear witness where their sensors can see (though laser and missile impacts on ships are reported system-wide, regardless of whether a ship you have in the system has sensors in the first place).