Difference between sensibility and threshold

Hi,

I am just trying to get my settings all working well and this has been really helpful.

When working with the threshold value does this consider only the area that is selected for motion detection or does it consider the whole picture? Ie if I had only 10 percent of the picture enabled for motion detection would the threshold relate to a percentage of this 10 percent? (Not the whole capture image)

Cheers,