I think you mean less than the last inch or so.
FWIW I just got back from lunch and:
I tried mine with my forearm both at the window level and gasket level - both worked - that is appx 4.5"
I then tried my hand only (across the knuckle) and that worked as well - appx 1.5".
I then tried pushing against the door while it was sliding. The door was about 10-12" away before it started to reverse.
I'm not brave enough (or stupid enough) to try just my finger.
My understanding is that the door will not reverse until the last 12" of travel.
From Day 1 our now almost 5 YO son has been told that the powers doors and any vehicles are off limits as places to play, explore, touch, etc. So far so good.
