When walking downstairs barefoot, I put the balls of my feet right on the edge of the step, so my toes overhang. Going upstairs I do the same thing, maybe a little farther into the step, so my heel hangs over the edge. In my head it’s a reflexive safety measure so I always have a good feel for where the edge is.
I don’t think about it, that’s just what I do.
I don’t do this with shoes on.