When reviewing the clips, I have lots of yellow boxes showing that it is sensing me, but it doesn't turn red unless I slow down. My settings are shown below. I've tried Gaussian and Simple, same result.
try it when you're running naked across the yard. that's what I do. Get back to us with your results.
Seriously though, the way "I approach it" is that your contrast is what we normally think of as "sensitivity". Min object size is used for differentiating between a squirrel and an elephant. Right now, (I think), you've got it set so that something needs to be the size of an aircraft carrier coming across your yard to make it trigger.