Basically, the issue is not so much "photography lens" work then perspective. From the moment you start using stadia-ranging, even if it is a crude "My Mark I eyeball says it is about Xm", you are assuming that the makers have kept things in perspective so it looks "natural" to the viewer, so their perspective is not all out of whack.
Spoiler for Long:
We thus assume they are using "normal" focal lengths, which are supposed to produce images close to our natural perspective. For 35mm media, this actually ranges from 35-85mm, corresponding to horizontal FOVs from 54.4 degrees down to 23.9.
There's this huge range because "normal" is a complicated subject. A camera is not an eyeball - for one thing, it has a much narrower FOV. Thus, normal is often a compromise. For example, cinematographers consider narrower FOVs (near 85mm) normal than photographers because a cinematographer expects his audience to view his masterpiece from a greater distance (being in a cinema and all) and that produces a different perspective. BUt is that narrow FOV really so close to what your eye sees?
For a still 35mm camera, the theoretical normal is considered to be ~43mm, corresponding to a horizontal FOV of 45 degrees. Yet the typical camera "normal" lens is often set at 50mm (39.6 degrees) because a slightly telescopic lens is supposed to be easier to make. But you can also say that 35mm is "normal" because it is still reasonably close to the perspective normal (if you can round up by 7 to 50mm, why not round down by 8 to 35mm?) and it is more "normal" in another sense - it provides a wider FOV which is closer to what an eye actually sees.
So the whole natural perspective is complicated, and even granted that 7Arcs is not trying to screw us, it is hard to tell what set of considerations they used to give us the "natural" perspective. Nevertheless, 35-85mm is the typical arc of "normal", so I assume (have to assume so I can get something useful out of stadia ranging) they use a focal length somewhere inside this.
As for local terrain, it can be used but it is also iffy. How big is a terrain feature. If two combatants are ten houses apart, are the houses 10m across or 20?
----------------------------------------------------------------------------------
UPDATE: I've went and gotten the screenshots. Please refer here for details:
http://arkhangelsk.onlinewebshop.net/mglnss12.html
Short version is that you seemed to have guessed roughly right on the speed despite your inappropriate methodology, but the range, well it WAS longer than 100 but it probably isn't what you want it to be either.