Supreme Ruler has two different line of sight systems.
The Simplified (?) system and the Advanced (aka Fuzzy ) system.
The Simplified system only takes into consideration the distance of a units and the spotting range of the spotter.
If the unit is in range of the spotting units then it automatically means that this unit is detected.
The Advanced system also takes into account the spotting strength of the spotter and the stealth strength of the unit. Should the stealth strength of the unit be too high then the spotter might have no chance at all to detect the unit. But usually a high stealth strength (relative to the spotting strength of the spotter) means that a unit has to come closer to detect the unit.
So effectively stealth strength reduces the spotting range of a spotting unit.