DracoSuave
First Post
One thing you forgot, DracoSuave, is that you can actively perceive something on your turn. This is a Perception roll against the creature's last Stealth check (presumably, the one that beat your Passive Perception to become hidden from you).
In cases where the opponent is actually hidden (i.e. they used Stealth) then obviously you can attempt Perception. But in the case where they are not, I strongly suggest not giving the guy you can't see additional benefit by requiring a further test of their perception; Either the enemy is not bothering/broke stealth, or the enemy failed their stealth check against Passive Perception -10.
The -10 to checks for being blind DOES apply to Passive Perception, as it is considered a check where you take 10. And if the enemy failed stealth that badly, they shouldn't get benefit.