I was sort of going at it from a different direction.
First, IIRC, some of the AFFS survivors hid in caves?
Second, you can tell how rugged the wilderness- and how widespread- it is based on how much men & material were able to hide out there during the Drac occupation. A battalion out of all those shattered regiments? Less trees, flatter (think Whichita Mtns), more open, fewer caves, and less available food. Enough men to fill three regiments? Lots of mature forest with mixed hardwoods & pine, lots of broken up terrain (think Appalachins), metal/coal mines w/caves, and edible plants/fishing/hunting along with ease of sneaking food out of farming zones to the resistance group. Enough men to fill five infantry regiments? Heavily forested, very rugged mountains (think Rockies), lots of mining activity, extensive cave zones based off limestone layers, and since that terrain is contra-indicated for farming, the resistance can absolutely support whatever supplies they fled with from the Dracs w/farmer support. Or fishing fleets, getting fish inland might be easier than produce.
How many years were they hiding in the boonies? How large was the Drac garrison- whose sport should have been hunting bands of AFFS survivors?
TLDR- It is easier to hide bands of surviving troops in the Rockies than Saskatchewan; more troops that survived the occupation = more rugged terrain.
