Home layout may influence the answer, but I can see no reason why anyone would ever want to "stay guard at top of stairs."
One's objectives should be to stay safe, to keep everyone in the family safe; to avoid confrontation if possible, and to be able to employ deadly force successfully as a last reort without getting hurt, if and only if it cannot be avoided.
On'e objective is not to ambush someone because of their intentions.
If I have time to choose a defensive location, it will be behind cover behind a closed door.
I have no reason to expect that I would be able choose my location, however.