Nah, dun complicate programming..... If its within range, u see him. If not, its off the radar range. Period. 
It was meant to help you find the last alien, a thing someone said to be a problem. Complicated? Yes but more enjoyable than looking through every corner in the map. Though if the AI is going to be changed, I guess this is not going to be a problem anymore and this concept can be abandoned.
