Possibly more interesting is where you've put the centre of the arc, half way up the left hand side. As I hold mine, the centre would be over the bottom right c

Possibly more interesting is where you've put the centre of the arc, half way up the left hand side. As I hold mine, the centre would be over the bottom right corner of the screen, and at "maximum extension" my thumb is just over the top left corner. (I've got "Nash equilibrium" in the back of my head writing this... if I couldn't reach the whole screen, I'd probably change the way I hold my phone.)