Perhaps it is intended that players figure it out for themselves, but it would help to be more clear about which distances correspond to which color. And apparently being adjacent on the next row is not "as close" as being adjacent on the same row. I had assumed that there would be an equal radius covering the same color.
It's based on the measured distance between the centers of the keys, so since the keys are taller than they are wide, it's a shorter distance between horizontal keys than vertical. As for informing the user about what colors mean, that was what the examples were meant to indicate: Q is as far as possible, and U is as close as possible (horizontally adjacent). But as was suggested I'm going to try adding a gauge next to the game board so it's more clear