Given the ranges in CT, if you are behind a planet, you're far enough away that an intercept is going to be obvious.Always? Do you ever have your NPCs or the Travellers go cold, hide behind moons, etc... to try and get the jump on their target?
CT sensors have detect 2 Light Seconds of range for military, and ½LS for civil. (TTB 75) 1G for one turn is 1/30 light second per turn. Either can maintain a 3 LS sensor track.
Maximum laser range is 1 2/3 LS (requires gunner interact or predict program running).