Although I have had several equatorial mounts, and although all will go through Polaris, anything closer than around 8° radial from Polaris is almost impossible to track as a small mechanical deviation X or Y will be impossible to allocate with any certainty to RA and DEC in correct proportions - things would rapidly go awry.
I suspect that there is a hard limit but it will likely be slightly over the zenith and that the limit experienced is soft. My other Smart scope - Unistellar - certainly reaches just past zenith - it parks lens up at zenith rather than lens down like this one!