Geometrically 50% of the movement does nothing (going left is a null action). In terms of distance moved by the pointer it would be more efficient to arrange the options as a circle around the pointer, with maybe the bottom 10% of the circle used for the null action
A possible benefit is 90% of the screen could then be used to display a larger set of options, which could let the user bisect their choices more quickly
That is an interesting idea! The space of possible next characters expands polynomially, so as you say, the display might be better used with a polar grid compared to cartesian.
