We used to have ours at top of stairs but them when our little girl went into her big bed she kept getting up and coming out her room and it turned into a game for her and one night I went up and found her asleep in the cats bed on the landing!! Lol! Was funny at time but it got frustrating and bed time got later and later!
So, we moved it to her bedroom door. If she needs me in the night, most of the time she just sits up in her bed and calls me or I hear her open her door. Since she knows she stays in bed at bed time she never comes to the door, only if she's woken up for the morning.
If we're upstairs and I'm having a shower, she just plays in her room with the bedroom door open and the gate shut. She's quite happy to do this.
Also if I'm just about upstairs cleaning she just follows me around but she's very good and knows not to go downstairs without me, still, I keep my eye on her, normally she's helpings clean anyways! ;-)