Question regarding thermographic perception, Just how impressive is it? Options

[Kurukami]

There's a particular character in a campaign I'm in, a troll mage with a security helmet decked out with all the nifty toys (among them magnification). Recently he got sniped at from behind/the side (out of his initial field of vision). The player then turned and asked whether or not he could spot where the shot came from, given that he had thermo and visual magnification to spot the heat from the muzzle plume.

Keep in mind this sniper was something like 800 meters away, and this was in a city environment with tons of other visual clutter.

So here's the question: would you allow the character in question to quickly spot the precise spot where the shot came from and, on his next action, stunbolt the sniper. Said sniper would presumably would be under cover/concealment, and nearly a klick away.