A person with 20/20 vision can distinguish contours about 2mm apart at 6 meters distance. At 1800 meters, you'd be doing well to identify features that were half a meter across. At the horizon, it'd be difficult to distinguish a 'Mech in a field from a lone tree.
That suggests distinguishing a laser aperture from an autocannon muzzle should be possible around 25-30 hexes with the naked eye. A Hunchback could be distinguished from a Swayback (by the absence of the shoulder pod) somewhere around 1-1.5km using unaided vision.
If zoom optics are available, increase those ranges by the power of the zoom. A not-unreasonable 24X magnification (typical long-range rifle scope) would let you ID a Hunchback at the horizon (atmospheric haze and refraction notwithstanding).
That strongly suggests the sight ranges ingame are either not using magnification, or are greatly contracted.
