The factors are these:
Pop size: There is an inverse relationship. Camps are more likely to spot an alien than cities. Semi-rural people know their neighbors.
Pop loyalty. The more loyal the population the more likely they are to report strangers.
Relations: You are more likely to see characters of nations you hate than nations you are friendly with. This can be seen currently in the U.S. Persons who look Middle-Eastern are noticed and observed while Englishmen are ignored.
Character skill ranks. All skills are counted and cumulative. Elrond stands out like a Klansman at an NAACP convention wherever he goes.
Skill artifacts. If you wear a helm-of-command you tend to get noticed.
Stealth. Has a subtractive effect. How much is hotly debated.
Well, the only Comms I send to enemy pops are either carrying the banner or leading the company of agents and aren’t high enough to be spotted by his own cousin…designed that way, in fact. Mages likewise, are either on their own pops training, scurrying about scouring through dung heaps on the plains, or 1 hex away… The emissaries can be explained in my experience as they’re the only characters who ever get stealth.
This order allows a Character to scout for any other Nation’s
Characters at that land location. Success is based on a comparison of
the relative Agent ranks and is chances are increased by the presence
of a Population Centre (camp the most, city the least). It is possible to
gain the following information on each Character found: title, name
or gender, and nationality or allegiance. The amount and detail of the
reported information is based on the Agent rank and incorrect reports
are possible.
This is the direct Rules quote. Now the part that I bolded always catches my eye. To me that reads that it comparest the Rank of the Agent doing the order against the Agent rank of the people in the Hex. Thus…people with Agent rank are harder to find. Which can make sense if you think about the fact that Agents are supposed to be sneaky.