I don't think the pushing should be calculated by the strength of a person, nor the weight, nor anything related to the person, since noobs will have no chance at all. I much prefer the things about staying in one place for X amount of time without doing anything disables it. I thought maybe 30 seconds, because then, if someone stops in a door way, it is only 30 seconds to wait until a person can walk through him. Of course, as soon as the person talks, attacks, eats, drinks, or dose anything, the collision system would be reactivated...