Wow.
As an ex Army man, I can tell you that the average range of most contacts with the enemy (from WW2 onwards through Korea, Vietnam, Iraq and Afghanistan) are under 30 m (60 odd foot).
Forgive my skepticism, but my understanding from reading Army papers on engagement ranges in Afghanistan is that the typical firefight in Afghanistan occurs at ranges of about a kilometer (due to range limitations on weaponry). Urban fights in Iraq were much closer, on the order of 100m, but if you're claiming that Afghanistan fights average 30m then I just don't believe you know better than the Army does. Sorry if I'm misunderstanding your claim.
BTW, you seem a bit confused on the ratio between meters and feet. 30 meters is 100 odd feet, not 60.
In very open and mountainous terrain (i.e. where you are on higher ground, and there is no terrain or cover for your enemy to hide behind, such as Afghanistan) engagement distance can be pushed out to half a mile or so (around 800m) away but that is generally very rare indeed.
This bears out in my practical experience as well.
Seriously. Walk outside and tell me if you can see a mile (1600 meters) in any one direction.
Here in Washington it's hilly enough that I often can only see half a mile. Sometimes I can see a mile or more, along roads, when it's either flat or elevated terrain. And that's without even deliberately trying to gain elevation, like I would if I were, say, a PC who is actively expecting life-and-death struggles and has a vested interest in knowing who or what is around to kill him. There's a reason the DMG gives standard visibility range as 1-2 miles.
Try it again when you are next out in urban, woods, forest, scrub, hills, swamp etc etc.... basically anywhere outside. Its next to impossible.
In anything less than a situation where you are on top of some high terrain and looking down into a valley (or looking over a large lake, dead flat desert, or out at sea) you are not going to bump into anyone until you're (within less than a hundred foot) or so. *snip* Seriously; people [even trained scouts and SF soldiers] don't generally look at what's a mile in front of them. Humans only generally scan 100' and closer, with a focus on objects that are within the closest 20 or so feet.
I don't know about you, but I scan at least 500' ahead of me even when I'm just casually
driving, not even fighting for my life. You keep talking as if PCs spend all their time in thickets and undergrowth; I'll agree that 1 mile is not a realistic encounter distance for forested terrain, but when I said that I start many or most encounters at distances of 1 mile (absent Stealth) you can then infer that my campaign
doesn't happen in a thick forest. Furthermore, when PCs are travelling, they generally travel through open terrain instead of through thick forest because it is faster. The same factors that lead to faster travel also support higher visibility.
When one or both parties try to employ Stealth, engagement ranges at my table shrink considerably, so combat won't occur until someone fails Stealth, even if the encounter "started" further out. Each successful Stealth roll gets you half the remaining distance to the enemy without being spotted. Potentially they might never notice each other at all.
And I just flat out don't share your apparent belief that an SF scout or veteran PC won't generally notice a large body of non-stealthy enemy troops until they get within 100' of him. That is shorter than my driveway!