Trigger implementation

Hi,

I want to know how Unity developers have implemented the trigger functionality.

I came across this question after running through an issues. Actually what I figured was that if 5% of the object was overlapping the trigger area it did not fired any trigger and only fired if the amount of overlap was greater than that. I am asking this because I want to know if our assumption (trigger works only if collision is greater than a certain threshold) is correct or is there anything else.

NOTE: I was using character controller on my character with skin width set to 0.001.