Of the 3 in my test, 2 were set at maximum, the other was at the default (middle setting). I was literally walking around them, waving my arms, etc. I think it is just that they have a 3-4 minute delay before detecting motion after they last sense it (which doesn’t make sense - no pun intended :^)
I think when you arm the system (either Home or Away), the sensors should arm after the exit delay period you set. Ours is 30 seconds.