egghead presence. how it works?

[pietro_moog]

hi guys. i'm thinking about building an egghead overdrive, but i wanted to understand how the presence pot works.
it doesn't seem like the bass control on the timmy or the voice control on the zen drive.
what does it do? does it affect the overall gain? how? the potentiometer and the resistor in the feedback loop form a voltage divider with the leg resistor, and that makes an hi pass filter with the cap after it. this i know.
why the pot is after the capacitor?