It's based on the following principles:
- I've found an appropriate velocity range on my Kawai NV5s to be from 8 to 113 (per calibration tool in Pianoteq)
- Without particular effort to play either very loudly or softly, this curve maps my keypresses nicely within the p to mf range as I think is appropriate
- This brings out a lot of touch responsiveness within that p - mf range that makes for lively playing, though it can be too much if you don't play evenly (which has been my experience on acoustics)

That's a smoothed version of this simpler one that I made first:
Velocity = [0, 8, 36, 55, 77, 113, 127; 0, 0, 32, 70, 98, 127, 127]