A subsection of STATIONARY PLAYERS Ref, pdf page 15.
Player pdf page 48HIDDEN CAMP: If the PCs make no attempt to hide their camp, approaching NPCs will automatically spot it. If the
PCs do hide their camp, roll RECON as described on page xx of the Players’ Manual. If the NPCs fail to spot the camp, the PCs can choose whether to stay undetected or make their presence known.
It's not totally unambigious, but it can be interpreted as if the enemy needs a succesful RECON if the PCs are hiddenRECON (INT)
Use the RECON skill to spot concealed enemies, avoid ambushes, move silently and avoid being detected. Make an opposed roll (page xx) against your adver- sary’s RECON. If you win, you manage to avoid being spotted.
The person or group trying to stay hidden is always the active party in the opposed roll, i.e. they must roll more than the opponent to remain undetected, and only they can push the roll. Read more about stealth and ambushes on page xx.
You can also use RECON when traveling, to spot an- other party on the trail before they spot you. See chap- ter 6.
Edit: still doesn't make sense why encounters becomes more severe over time. and why enemies discover that they have been spotted etc