Real world stealth works off a combination of factors, but since Elite doesn't use Radar in any traditional sense (which, given the distances involved, makes sense) the most effective real-world stealth technique that would be applicable to Elite is probably something as simple as engine placement. In the B-2, for example, the engines are placed on the top side of the plane and mid-wing (and there is also some other stuff like maxing in cool air into the exhaust to enhance this.) What this translates to is that the plane is near-invisible from the ground, but from above it's far less stealthy (though, again, this in on Earth where Radar is the primary means of detection.)
In Elite, it'd make sense for the stealth of a ship to be determined not just by heat level, but also by engine placement and direction of facing. A properly vented ship facing towards its target that is not firing maneuvering thrusters should be invisible, night vision or not, and for that matter, regardless of heat level. As the angle of viewing increases and more of the exhaust can be seen, the ship should be detectable at farther and farther ranges. From directly behind the engines at full throttle would be the most detectable. This is even more true in Elite than real life, as there is no air friction to heat up the body of a spacecraft, so nearly all of the heat generated is vented out as exhaust, whereas airplanes often have just as much heat buildup from air friction as they do from exhaust.
I guess what I'm saying is that the heat/stealth model in Elite is, like the flight model, inspired by real life but clearly not bound to it. Even FA-Off isn't perfect Newtonian physics (it's close, but FA-off within a planet's gravity well and you will not accelerate towards the planet like you technically should.) So I'd like to see stealth improved too, but given the way it currently works it'd be a pretty large rework to really make it work properly.
