Perception check obstacles

Can anyone can give me some benchmarks on perception check obstacles?

When in doubt, I usually start with BWG page 15. I think we tend to use Ob 3 for stuff anyone could credibly notice or figure out, and Ob 5 for “Surprise! No one knew this was here!” kind of stuff.

Concrete situations in our game:
Find an opportunity to create a diversion (in a non-militarized camp). Ob 3.
A magic eel thing whispers in your ear. Can you make out what it’s saying? Ob 2.
Find hidden treasure in an abandoned old monastery. Ob 5.
Wander around town gathering information, then have an “Aha!” moment by correlating two bits of data when you doodle a crude map in the dirt. Ob 5.
With Manhunter trait: Ob 2 to read mood, Ob 4 to read intent (are these guys gonna betray me?), Ob 6 to read instincts, Ob 7 to read beliefs. (These are lifted from the Aura Reading skill.)
Also with Manhunter: is that one of your friends trapped in a magic dream with you, or just a dream version of one of them? Ob 3, based on “read a character trait.”
Also with Manhunter: read the beliefs of a weird magical being with an inhuman mindset. Ob 9. I.e. a base of 7 with +2 Ob for being a weird magical being with an inhuman mindset.